Chemical-free production of graphene-wrapped electrode active material particles for battery applications

ABSTRACT

Provided is a simple, fast, scalable, and environmentally benign method of producing graphene-embraced or encapsulated particles of a battery electrode active material directly from a graphitic material, the method comprising: a) mixing graphitic material particles, multiple particles of an electrode active material, and non-polymeric particles of milling media to form a mixture in an impacting chamber, wherein the graphitic material has never been intercalated, oxidized, or exfoliated and the chamber contains therein no previously produced graphene sheets; b) operating the energy impacting apparatus with a frequency and an intensity for a length of time sufficient for peeling off graphene sheets from the graphitic material and transferring graphene sheets to surfaces of electrode active material particles to produce graphene-embraced active material particles; and c) recovering the graphene-embraced particles from the impacting chamber. Also provided is a mass of the graphene-embraced particles, electrode containing such particles, and battery containing this electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of the U.S. patentapplication Ser. No. 15/156,504 (May 17, 2016), the contents of whichare incorporated by reference herein, in their entirety, for allpurposes.

FIELD OF THE INVENTION

The present invention relates generally to the field of lithiumbatteries and, in particular, to an environmentally benign andcost-effective method of producing graphene-protected electrode activematerials for lithium batteries.

BACKGROUND A Review on Anode Active Materials

The most commonly used anode materials for lithium-ion batteries arenatural graphite and synthetic graphite (or artificial graphite) thatcan be intercalated with lithium and the resulting graphiteintercalation compound (GIC) may be expressed as Li_(x)C₆, where x istypically less than 1. The maximum amount of lithium that can bereversibly intercalated into the interstices between graphene planes ofa perfect graphite crystal corresponds to x=1, defining a theoreticalspecific capacity of 372 mAh/g.

Graphite or carbon anodes can have a long cycle life due to the presenceof a protective surface-electrolyte interface layer (SEI), which resultsfrom the reaction between lithium and the electrolyte (or betweenlithium and the anode surface/edge atoms or functional groups) duringthe first several charge-discharge cycles. The lithium in this reactioncomes from some of the lithium ions originally intended for the chargetransfer purpose. As the SEI is formed, the lithium ions become part ofthe inert SEI layer and become irreversible, i.e. they can no longer bethe active element for charge transfer. Therefore, it is desirable touse a minimum amount of lithium for the formation of an effective SEIlayer. In addition to SEI formation, the irreversible capacity lossQ_(ir) can also be attributed to graphite exfoliation caused byelectrolyte/solvent co-intercalation and other side reactions.

In addition to carbon- or graphite-based anode materials, otherinorganic materials that have been evaluated for potential anodeapplications include metal oxides, metal nitrides, metal sulfides, andthe like, and a range of metals, metal alloys, and intermetalliccompounds that can accommodate lithium atoms/ions or react with lithium.Among these materials, lithium alloys having a composition formula ofLi_(a)A (A is a metal such as Al, and “a” satisfies 0<a #5) are of greatinterest due to their high theoretical capacity, e.g., Li₄Si (3,829mAh/g), Li_(4.4)Si (4,200 mAh/g), Li_(4.4)Ge (1,623 mAh/g), Li_(4.4)Sn(993 mAh/g), Li₃Cd (715 mAh/g), Li₃Sb (660 mAh/g), Li_(4.4)Pb (569mAh/g), LiZn (410 mAh/g), and Li₃Bi (385 mAh/g). However, in the anodescomposed of these materials, severe pulverization (fragmentation of thealloy particles) occurs during the charge and discharge cycles due toexpansion and contraction of the anode active material induced by theinsertion and extraction of the lithium ions in and out of the anodeactive material. The expansion and contraction, and the resultingpulverization of active material particles lead to loss of contactsbetween active particles and conductive additives and loss of contactsbetween the anode active material and its current collector. Thisdegradation phenomenon is illustrated in FIG. 1. These adverse effectsresult in a significantly shortened charge-discharge cycle life.

To overcome the problems associated with such mechanical degradation,three technical approaches have been proposed:

-   (1) reducing the size of the active material particle, presumably    for the purpose of reducing the strain energy that can be stored in    a particle, which is a driving force for crack formation in the    particle. However, a reduced particle size implies a higher surface    area available for potentially reacting with the liquid electrolyte.    Such a reaction is undesirable since it is a source of irreversible    capacity loss.-   (2) depositing the electrode active material in a thin film form    directly onto a current collector, such as a copper foil. However,    such a thin film structure with an extremely small    thickness-direction dimension (typically much smaller than 500 nm,    often necessarily thinner than 100 nm) implies that only a small    amount of active material can be incorporated in an electrode (given    the same electrode or current collector surface area), providing a    low total lithium storage capacity and low lithium storage capacity    per unit electrode surface area (even though the capacity per unit    mass can be large). Such a thin film must have a thickness less than    100 nm to be more resistant to cycling-induced cracking, further    diminishing the total lithium storage capacity and the lithium    storage capacity per unit electrode surface area. Such a thin-film    battery has very limited scope of application. A desirable and    typical electrode thickness is from 100 μm to 200 μm. These    thin-film electrodes (with a thickness of <500 nm or even <100 nm)    fall short of the required thickness by three (3) orders of    magnitude, not just by a factor of 3.-   (3) using a composite composed of small electrode active particles    protected by (dispersed in or encapsulated by) a less active or    non-active matrix, e.g., carbon-coated Si particles, sol gel    graphite-protected Si, metal oxide-coated Si or Sn, and    monomer-coated Sn nanoparticles. Presumably, the protective matrix    provides a cushioning effect for particle expansion or shrinkage,    and prevents the electrolyte from contacting and reacting with the    electrode active material. Examples of anode active particles are    Si, Sn, and SnO₂. Unfortunately, when an active material particle,    such as Si particle, expands during the battery charge step, the    protective coating is easily broken due to the mechanical weakness    and/or brittleness of the protective coating materials. There has    been no high-strength and high-toughness material available that is    itself also lithium ion conductive.

It may be further noted that the coating or matrix materials used toprotect active particles (such as Si and Sn) are carbon, sol gelgraphite, metal oxide, monomer, ceramic, and lithium oxide. Theseprotective materials alone are all very brittle, weak (of low strength),and/or non-conducting (e.g., ceramic or oxide coating). Ideally, theprotective material should meet the following requirements: (a) Thecoating or matrix material should be of high strength and stiffness sothat it can help to refrain the electrode active material particles,when lithiated, from expanding to an excessive extent. (b) Theprotective material should also have high fracture toughness or highresistance to crack formation to avoid disintegration during repeatedcycling. (c) The protective material must be inert (inactive) withrespect to the electrolyte, but be a good lithium ion conductor. (d) Theprotective material must not provide any significant amount of defectsites that irreversibly trap lithium ions. (e) The protective materialmust be lithium ion conductive. The prior art protective materials allfall short of these requirements. Hence, it was not surprising toobserve that the resulting anode typically shows a reversible specificcapacity much lower than expected. In many cases, the first-cycleefficiency is extremely low (mostly lower than 80% and some even lowerthan 60%). Furthermore, in most cases, the electrode was not capable ofoperating for a large number of cycles. Additionally, most of theseelectrodes are not high-rate capable, exhibiting unacceptably lowcapacity at a high discharge rate.

Due to these and other reasons, most of prior art composite electrodeshave deficiencies in some ways, e.g., in most cases, less thansatisfactory reversible capacity, poor cycling stability, highirreversible capacity, ineffectiveness in reducing the internal stressor strain during the lithium ion insertion and extraction steps, andother undesirable side effects.

Complex composite particles of particular interest are a mixture ofseparate Si and graphite particles dispersed in a carbon matrix; e.g.those prepared by Mao, et al. [“Carbon-coated Silicon Particle Powder asthe Anode Material for Lithium Batteries and the Method of Making theSame,” US 2005/0136330 (Jun. 23, 2005)]. Also of interest are carbonmatrix-containing complex nano Si (protected by oxide) and graphiteparticles dispersed therein, and carbon-coated Si particles distributedon a surface of graphite particles Again, these complex compositeparticles led to a low specific capacity or can be charged-dischargedfor up to a small number of cycles only. It appears that carbon byitself is relatively weak and brittle and the presence of micron-sizedgraphite particles does not improve the mechanical integrity of carbonsince graphite particles are themselves relatively weak. Graphite wasused in these cases presumably for the purpose of improving theelectrical conductivity of the anode material. Furthermore, polymericcarbon, amorphous carbon, or pre-graphitic carbon may have too manylithium-trapping sites that irreversibly capture lithium during thefirst few cycles, resulting in excessive irreversibility.

In summary, the prior art has not demonstrated a composite material thathas all or most of the properties desired for use as an anode materialin a lithium-ion battery. Thus, there is an urgent and continuing needfor a new anode for the lithium-ion battery that has a high cycle life,high reversible capacity, low irreversible capacity, small particlesizes (for high-rate capacity), and compatibility with commonly usedelectrolytes. There is also a need for a method of readily or easilyproducing such a material in large quantities.

In response to these needs, one of our earlier applications discloses ananoscaled graphene platelet-based composite composition for use as alithium ion battery anode [A. Zhamu and B. Z. Jang, “Nano GraphenePlatelet-Based Composite Anode Compositions for Lithium Ion Batteries,”U.S. patent application Ser. No. 11/982,672 (Nov. 5, 2007); Now U.S.Pat. No. 7,745,047 (Jun. 29, 2010)]. This composition comprises: (a)micron- or nanometer-scaled particles or coating of an anode activematerial; and (b) a plurality of nanoscaled graphene platelets (NGPs),wherein a platelet comprises a graphene sheet or a stack of graphenesheets having a platelet thickness less than 100 nm and wherein theparticles or coating are physically attached or chemically bonded toNGPs. Nano graphene platelets (NGPs) are individual graphene sheets(individual basal planes of carbon atoms isolated from a graphitecrystal) or stacks of multiple graphene planes bonded together in thethickness direction. The NGPs have a thickness less than 100 nm and alength, width, or diameter that can be greater or less than 10 μm. Thethickness is more preferably less than 10 nm and most preferably lessthan 1 nm.

Disclosed in another patent application of ours is a more specificcomposition, which is composed of a 3-D network of NGPs and/or otherconductive filaments and select anode active material particles that arebonded to these NGPs or filaments through a conductive binder [JinjunShi, Aruna Zhamu and Bor Z. Jang, “Conductive Nanocomposite-basedElectrodes for Lithium Batteries,” U.S. patent application Ser. No.12/156,644 (Jun. 4, 2008) (U.S. Pat. Pub. No. 2009-0305135)]. Yetanother application, as schematically shown in FIGS. 2(A) and 2(B),provides a nano graphene-reinforced nanocomposite solid particlecomposition containing NGPs and electrode active material particles,which are both dispersed in a protective matrix (e.g. a carbon matrix)[Aruna Zhamu, Bor Z. Jang, and Jinjun Shi, “Nano Graphene ReinforcedNanocomposite for Lithium Battery Electrodes,” U.S. patent applicationSer. No. 12/315,555 (Dec. 4, 2008) (U.S. Pat. Pub. No. 2010-0143798)].

After our discovery of graphene providing an outstanding support foranode active materials, many subsequent studies by others have confirmedthe effectiveness of this approach. For instance, Wang, et al.investigated self-assembled TiO₂-graphene hybrid nanostructures forenhanced Li-ion insertion [D. Wang, et al. “Self-Assembled TiO₂-GrapheneHybrid Nanostructures for Enhanced Li-Ion Insertion.” ACS Nano, 3 (2009)907-914]. The results indicate that, as compared with the pure TiO₂phase, the specific capacity of the hybrid was more than doubled at highcharge rates. The improved capacity at a high charge-discharge rate wasattributed to increased electrode conductivity afforded by a percolatedgraphene network embedded into the metal oxide electrodes. However, allthese earlier studies were focused solely on providing a network ofelectron-conducting paths for the anode active material particles andfailed to address other critical issues, such as ease of anode materialprocessing, electrode processability, electrode tap density (the abilityto pack a dense mass into a given volume), and long-term cyclingstability. For instance, the method of preparing self-assembled hybridnanostructures is not amenable to mass production. The graphene oxidesheets used were made using an environmentally undesirable process priorto the assembling procedure. The anode material particle-coated graphenesheets alone are not suitable for electrode fabrication (due to thedifficulty in coating the materials onto a current collector), and theresulting electrodes are typically too low in the tap density.Additionally, paper-based composite structures are not compatible withcurrent lithium-ion battery production equipment. These are allcritically important issues that must be addressed in a real batterymanufacturing environment.

A Review on Cathode Active Materials

Due to extremely poor electrical conductivity of all cathode (positiveelectrode) active materials in a lithium-ion, lithium metal, orlithium-sulfur cell, a conductive additive (e.g. carbon black, finegraphite particles, expanded graphite particles, or their combinations),typically in the amount of 5%-20%, must be added into the electrode. Inthe case of a lithium-sulfur cell, a carbon amount as high as 50% byweight is used as a conductive support for sulfur in the cathode.However, the conductive additive is not an electrode active material(i.e. it is not capable of reversibly storing lithium ions). The use ofa non-active material means that the relative proportion of an electrodeactive material, such as LiFePO₄, is reduced or diluted. For instance,the incorporation of 5% by weight of PVDF as a binder and 5% of carbonblack as a conductive additive in a cathode would mean that the maximumamount of the cathode active material (e.g., lithium cobalt oxide) isonly 90%, effectively reducing the total lithium ion storage capacity.Since the specific capacities of the more commonly used cathode activematerials are already very low (140-170 mAh/g), this problem is furtheraggravated if a significant amount of non-active materials is used todilute the concentration of the active material.

State-of-the-art carbon black (CB) materials, as a conductive additive,have several drawbacks:

-   -   (1) CBs are typically available in the form of aggregates of        multiple primary particles that are typically spherical in        shape. Due to this geometric feature (largest        dimension-to-smallest dimension ratio or aspect ratio−1) and the        notion that CBs are a minority phase dispersed as discrete        particles in an electrically insulating matrix (e.g. lithium        cobalt oxide and lithium iron phosphate), a large amount of CBs        is required to reach a percolation threshold where the CB        particles are combined to form a 3-D network of        electron-conducting paths.    -   (2) CBs themselves have a relatively low electrical conductivity        and, hence, the resulting electrode remains to be of relatively        low conductivity even when the percolation threshold is reached.        A relatively high proportion of CBs (far beyond the percolation        threshold) must be incorporated in the cathode to make the        resulting composite electrode reasonably conducting.

Clearly, an urgent need exists for a more effective electricallyconductive additive material. Preferably, this electrically conductiveadditive is also of high thermal conductivity. Such a thermallyconductive additive would be capable of dissipating the heat generatedfrom the electrochemical operation of the Li-ion battery, therebyincreasing the reliability of the battery and decreasing the likelihoodthat the battery will suffer from thermal runaway and rupture. With ahigh electrical conductivity, there would be no need to add a highproportion of conductive additives.

There have been several attempts to use other carbon nanomaterials thancarbon black (CB) or acetylene black (AB) as a conductive additive forthe cathode of a lithium battery. These include carbon nanotubes (CNTs),vapor-grown carbon nanofibers (VG-CNFs), and simple carbon coating onthe surface of cathode active material particles. The result has notbeen satisfactory and hence, as of today, carbon black and artificialgraphite particles are practically the only two types of cathodeconductive additives widely used in lithium ion battery industry. Thereasons are beyond just the obvious high costs of both CNTs and VG-CNFs.The difficulty in disentangling CNTs and VG-CNFs and uniformlydispersing them in a liquid or solid medium has been an impediment tothe more widespread utilization of these expensive materials as aconductive additive. Additionally, the production of both CNTs andVG-CNFs normally require the use of a significant amount of transitionmetal nanoparticles as a catalyst. It is difficult to remove andimpossible to totally remove these transition metal particles, which canhave adverse effect on the cycling stability of a lithium metal.

As for the less expensive carbon coating, being considered for use inlithium iron phosphate, the conductivity of the carbon coating(typically obtained by converting a precursor such as sugar or resin viapyrolyzation) is relatively low. It would take a graphitizationtreatment to render the carbon coating more conductive, but thistreatment requires a temperature higher than 2,000° C., which woulddegrade the underlying cathode active material (e.g., LiFePO₄).

As an alternative approach, Ding, et al investigated the electrochemicalbehavior of LiFePO₄/graphene composites [Y. Ding, et al. “Preparation ofnanostructured LiFePO₄/graphene composites by co-precipitation method,”Electrochemistry Communications 12 (2010) 10-13]. The co-precipitationmethod leads to the formation of LiFePO₄ nanoparticles coated on bothprimary surfaces of graphene nanosheets. The cathode is then prepared bystacking these LiFePO₄-coated graphene sheets together. This approachhas several major drawbacks:

-   -   (1) With the two primary surfaces of a graphene sheet attached        with LiFePO₄ nanoparticles, the resulting electrode entails many        insulator-to-insulator contacts between two adjoining coated        sheets in a stack.    -   (2) Only less than 30% of the graphene surface area is covered        by LiFePO₄ particles on either side. This is a relatively low        proportion of the cathode active material.    -   (3) The LiFePO₄ particles are easily detached from graphene        sheets during handling and electrode production.    -   (4) We have found that the nanoparticle-attached graphene sheets        as prepared by the co-precipitation method are not amenable to        fabrication of cathodes with current electrode coating        equipment. In particular, these particle-attached graphene        sheets could not be compacted into a dense state with a high        mass per unit electrode volume. In other words, the cathode tap        density is relatively low. This is a very serious issue since        all of the commonly used cathode active materials, including        LiFePO₄, already have a very low specific capacity (mAh/g), and        not being able to pack a large mass of a cathode active material        into a given electrode volume would mean an excessively low        overall capacity at the cathode side. (It may be noted that the        typical specific capacity (140-170 mAh/g) of a cathode active        material is already much lower than that (330-360 mAh/g) of an        anode active material. Such an imbalance has been a major issue        in the design and fabrication of lithium ion batteries.)

A Review on Graphene (Isolated Graphene Sheets or Nano GraphenePlatelets)

A single-layer graphene sheet is composed of carbon atoms occupying atwo-dimensional hexagonal lattice. Multi-layer graphene is a plateletcomposed of more than one graphene plane. Individual single-layergraphene sheets and multi-layer graphene platelets are hereincollectively called nano graphene platelets (NGPs) or graphenematerials. NGPs include pristine graphene (essentially 99% of carbonatoms), slightly oxidized graphene (<5% by weight of oxygen), grapheneoxide (≥5% by weight of oxygen), slightly fluorinated graphene (<5% byweight of fluorine), graphene fluoride ((≥5% by weight of fluorine),other halogenated graphene, and chemically functionalized graphene.

NGPs have been found to have a range of unusual physical, chemical, andmechanical properties. For instance, graphene was found to exhibit thehighest intrinsic strength and highest thermal conductivity of allexisting materials. Although practical electronic device applicationsfor graphene (e.g., replacing Si as a backbone in a transistor) are notenvisioned to occur within the next 5-10 years, its application as ananofiller in a composite material and an electrode material in energystorage devices is imminent. The availability of processable graphenesheets in large quantities is essential to the success in exploitingcomposite, energy, and other applications for graphene.

Our research group was among the first to discover graphene [B. Z. Jangand W. C. Huang, “Nano-scaled Graphene Plates,” U.S. patent applicationSer. No. 10/274,473, submitted on Oct. 21, 2002; now U.S. Pat. No.7,071,258 (Jul. 4, 2006)]. The processes for producing NGPs and NGPnanocomposites were recently reviewed by us [Bor Z. Jang and A Zhamu,“Processing of Nano Graphene Platelets (NGPs) and NGP Nanocomposites: AReview,” J. Materials Sci. 43 (2008) 5092-5101]. Our research hasyielded a process for chemical-free production of isolated nano grapheneplatelets that is novel in that is does not follow the establishedmethods for production of nano graphene platelets outlined below. Inaddition, the process is of enhanced utility in that it is costeffective, and provided novel graphene materials with significantlyreduced environmental impact. Four main prior-art approaches have beenfollowed to produce NGPs. Their advantages and shortcomings are brieflysummarized as follows:

Prior Art Method for Production of Isolated Graphene Sheets (NGPs)

Approach 1: Chemical Formation and Reduction of Graphite Oxide (GO)Platelets

The first approach (.1) entails treating natural graphite powder with anintercalant and an oxidant (e.g., concentrated sulfuric acid and nitricacid, respectively) to obtain a graphite intercalation compound (GIC)or, actually, graphite oxide (GO). [William S. Hummers, Jr., et al.,Preparation of Graphitic Oxide, Journal of the American ChemicalSociety, 1958, p. 1339.]Prior to intercalation or oxidation, graphitehas an inter-graphene plane spacing of approximately 0.335 nm(L_(d)=½d₀₀₂=0.335 nm). With an intercalation and oxidation treatment,the inter-graphene spacing is increased to a value typically greaterthan 0.6 nm. This is the first expansion stage experienced by thegraphite material during this chemical route. The obtained GIC or GO isthen subjected to further expansion (often referred to as exfoliation)using either a thermal shock exposure or a solution-based,ultrasonication-assisted graphene layer exfoliation approach.

In the thermal shock exposure approach, the GIC or GO is exposed to ahigh temperature (typically 800-1,050° C.) for a short period of time(typically 15 to 60 seconds) to exfoliate or expand the GIC or GO forthe formation of exfoliated or further expanded graphite, which istypically in the form of a “graphite worm” composed of graphite flakesthat are still interconnected with one another. This thermal shockprocedure can produce some separated graphite flakes or graphene sheets,but normally the majority of graphite flakes remain interconnected.Typically, the exfoliated graphite or graphite worm is then subjected toa flake separation treatment using air milling, mechanical shearing, orultrasonication in water. Hence, approach 1 basically entails threedistinct procedures: first expansion (oxidation or intercalation),further expansion (or “exfoliation”), and separation.

In the solution-based separation approach, the expanded or exfoliated GOpowder is dispersed in water or aqueous alcohol solution, which issubjected to ultrasonication. It is important to note that in theseprocesses, ultrasonification is used after intercalation and oxidationof graphite (i.e., after first expansion) and typically after thermalshock exposure of the resulting GIC or GO (after second expansion).Alternatively, the GO powder dispersed in water is subjected to an ionexchange or lengthy purification procedure in such a manner that therepulsive forces between ions residing in the inter-planar spacesovercome the inter-graphene van der Waals forces, resulting in graphenelayer separations.

There are several major problems associated with this conventionalchemical production process:

-   -   (1) The process requires the use of large quantities of several        undesirable chemicals, such as sulfuric acid, nitric acid, and        potassium permanganate or sodium chlorate.    -   (2) The chemical treatment process requires a long intercalation        and oxidation time, typically 5 hours to five days.    -   (3) Strong acids consume a significant amount of graphite during        this long intercalation or oxidation process by “eating their        way into the graphite” (converting graphite into carbon dioxide,        which is lost in the process). It is not unusual to lose 20-50%        by weight of the graphite material immersed in strong acids and        oxidizers.    -   (4) The thermal exfoliation requires a high temperature        (typically 800-1,200° C.) and, hence, is a highly        energy-intensive process.    -   (5) Both heat- and solution-induced exfoliation approaches        require a very tedious washing and purification step. For        instance, typically 2.5 kg of water is used to wash and recover        1 gram of GIC, producing huge quantities of waste water that        need to be properly treated.    -   (6) In both the heat- and solution-induced exfoliation        approaches, the resulting products are GO platelets that must        undergo a further chemical reduction treatment to reduce the        oxygen content. Typically even after reduction, the electrical        conductivity of GO platelets remains much lower than that of        pristine graphene. Furthermore, the reduction procedure often        involves the utilization of toxic chemicals, such as hydrazine.    -   (7) Furthermore, the quantity of intercalation solution retained        on the flakes after draining may range from 20 to 150 parts of        solution by weight per 100 parts by weight of graphite flakes        (pph) and more typically about 50 to 120 pph. During the        high-temperature exfoliation, the residual intercalate species        retained by the flakes decompose to produce various species of        sulfuric and nitrous compounds (e.g., NO_(x) and SO_(x)), which        are undesirable. The effluents require expensive remediation        procedures in order not to have an adverse environmental impact.        Approach 2: Direct Formation of Pristine Nano Graphene Platelets

In 2002, our research team succeeded in isolating single-layer andmulti-layer graphene sheets from partially carbonized or graphitizedpolymeric carbons, which were obtained from a polymer or pitch precursor[B. Z. Jang and W. C. Huang, “Nano-scaled Graphene Plates,” U.S. patentapplication Ser. No. 10/274,473, submitted on Oct. 21, 2002; now U.S.Pat. No. 7,071,258 (Jul. 4, 2006)]. Mack, et al [“Chemical manufactureof nanostructured materials” U.S. Pat. No. 6,872,330 (Mar. 29, 2005)]developed a process that involved intercalating graphite with potassiummelt and contacting the resulting K-intercalated graphite with alcohol,producing violently exfoliated graphite containing NGPs. The processmust be carefully conducted in a vacuum or an extremely dry glove boxenvironment since pure alkali metals, such as potassium and sodium, areextremely sensitive to moisture and pose an explosion danger. Thisprocess is not amenable to the mass production of NGPs.

Approach 3: Epitaxial Growth and Chemical Vapor Deposition of GrapheneSheets on Inorganic Crystal Surfaces

Small-scale production of ultra-thin graphene sheets on a substrate canbe obtained by thermal decomposition-based epitaxial growth and a laserdesorption-ionization technique. [Walt A. DeHeer, Claire Berger, PhillipN. First, “Patterned thin film graphite devices and method for makingsame” U.S. Pat. No. 7,327,000 B2 (Jun. 12, 2003)] Epitaxial films ofgraphite with only one or a few atomic layers are of technological andscientific significance due to their peculiar characteristics and greatpotential as a device substrate. However, these processes are notsuitable for mass production of isolated graphene sheets for compositematerials and energy storage applications.

Approach 4: The Bottom-Up Approach (Synthesis of Graphene from SmallMolecules)

Yang, et al. [“Two-dimensional Graphene Nano-ribbons,” J. Am. Chem. Soc.130 (2008) 4216-17] synthesized nano graphene sheets with lengths of upto 12 nm using a method that began with Suzuki-Miyaura coupling of1,4-diiodo-2,3,5,6-tetraphenyl-benzene with 4-bromophenylboronic acid.The resulting hexaphenylbenzene derivative was further derivatized andring-fused into small graphene sheets. This is a slow process that thusfar has produced very small graphene sheets.

Thus, an urgent need exists to have a graphene production process thatrequires a reduced amount of undesirable chemical (or elimination ofthese chemicals all together), shortened process time, less energyconsumption, lower degree of graphene oxidation, reduced or eliminatedeffluents of undesirable chemical species into the drainage (e.g.,sulfuric acid) or into the air (e.g., SO₂ and NO₂). The process shouldbe able to produce more pristine (less oxidized and damaged), moreelectrically conductive, and larger/wider graphene sheets.

Using the lithium-ion battery and lithium metal battery as examples,these graphene sheets must be effective in (a) protecting anode activematerials or cathode active materials (e.g. against volumeexpansion/shrinkage-induced pulverization) and the electrodes (againstexcessive volume changes of both anode and cathode) during repeatedbattery charges/discharges for improved cycle stability and (b)providing a 3D network of electron-conducting pathways without the useof an excessive amount of conductive additives that are non-activematerials (those that add weight and volume to the battery withoutproviding additional lithium-storing capacity).

Most desirably, a need exists for a process that is capable of producingisolated graphene sheets directly from a graphitic material and,concurrently, transferring the graphene sheets to wrap around or embracethe particles of an anode active material or cathode active material.

In short, the present invention was made to overcome the aforementionedlimitations of current lithium batteries and the graphene materials usedto protect these batteries.

SUMMARY OF THE INVENTION

The present invention provides a strikingly simple, fast, scalable,environmentally benign, and cost-effective method of producinggraphene-embraced (graphene-encapsulated) electrode active material(either an anode active material or a cathode active material) for awide variety of batteries. This method meets the aforementioned needs.This method entails producing single-layer or few layer graphene sheetsdirectly from a graphitic or carbonaceous material (a graphene sourcematerial) and immediately transferring these isolated (peeled-off)graphene sheets onto surfaces of electrode active material particles toform graphene-embraced or graphene-encapsulated electrode activematerial particles. In an embodiment, the graphitic material orcarbonaceous material has never been intercalated, oxidized, orexfoliated and does not include previously produced isolated graphenesheets.

Specifically, this invention provides a self-embracing orself-encapsulating method of producing a graphene-embraced orgraphene-encapsulated electrode active material directly from agraphitic material. In an embodiment, the method comprises:

-   -   a) mixing multiple particles of a graphitic material, multiple        particles of a solid electrode active material, and particles of        a non-polymeric ball-milling media to form a mixture in an        impacting chamber of an energy impacting apparatus, wherein the        graphitic material has never been intercalated, oxidized, or        exfoliated and does not include previously produced isolated        graphene sheets;    -   b) operating the energy impacting apparatus with a frequency and        an intensity for a length of time sufficient for transferring        graphene sheets from the particles of graphitic material to        surfaces of the solid electrode active material particles to        produce a graphene-embraced electrode active material inside the        impacting chamber (i.e., solid electrode active material        particles impinge upon surfaces of graphitic material particles,        peeling off graphene sheets therefrom, and naturally allowing        the peeled-off graphene sheets to fully wrap around or embrace        the solid electrode active material particles); and    -   c) recovering the particles of graphene-embraced electrode        active material from the impacting chamber and separating the        non-polymeric ball-milling media from particles of        graphene-embraced electrode active material.        The method further comprises a step of incorporating the        graphene-embraced or graphene-encapsulated electrode active        material into a battery electrode.

The non-polymeric particles of ball-milling media may contain millingballs selected from ceramic particles, metal oxide particles, metalparticles, glass particles, or a combination thereof. Metal particlesthat are ferromagnetic or are capable of being attracted to a magneticfield are particularly desired since they can be more readily or easilyremoved or separated from the graphene-coated electrode active materialsthat are normally non-magnetic.

There can be some particles of graphitic material that are not fullyutilized (i.e., not all graphene sheets have been peeled off) after stepb). Hence, in an embodiment, an amount of residual graphitic materialremains after step b) and the method further comprises a step ofincorporating the graphene-embraced electrode active material and theresidual graphitic material into a battery electrode. The residualgraphitic material can serve as a conductive filler in the batteryelectrode.

In another embodiment, an amount of residual graphitic material remainsafter step b), and step c) includes a step of partially or completelyseparating the residual amount of graphitic material from thegraphene-embraced electrode active material.

In some embodiments, the particles of solid electrode active materialcontain prelithiated or pre-sodiated particles. In other words, beforethe electrode active material particles (such as Si or SnO₂) areembraced by graphene sheets, these particles have been previouslyintercalated with Li or Na ions (e.g. via electrochemical charging) upto an amount of 0.1% to 30% by weight of Li or Na. This is a highlyinnovative and unique approach for the following considerations. Theintercalation of these particles with Li or Na has allowed the Si orSnO₂ particles to expand to a large volume (potentially up to 380% ofits original volume). If these prelithiated or pre-sodiated particlesare then wrapped around or embraced by graphene sheets and incorporatedinto an electrode (i.e. anode containing graphene-embraced particles ofSi or SnO₂), the electrode would no longer have any issues of electrodeexpansion and expansion-induced failure during subsequentcharge-discharge cycles of the lithium- or sodium-ion battery. In otherwords, the Si or SnO₂ particles have been provided with expansion spacebetween these particles and the embracing graphene sheets. Ourexperimental data have surprisingly shown that this strategy leads tosignificantly longer battery cycle life and more efficient utilizationof the electrode active material capacity.

In some embodiments, prior to the instant “graphene transfer andembracing process,” the particles of solid electrode active materialcontain particles pre-coated with a coating layer of a conductivematerial selected from carbon, pitch, carbonized resin, a conductivepolymer, a conductive organic material, a metal coating, a metal oxideshell, or a combination thereof. The coating layer thickness ispreferably in the range from 1 nm to 20 μm, preferably from 10 nm to 10μm, and further preferably from 100 nm to 1 μm.

In some embodiments, the particles of solid electrode active materialcontain particles that are pre-coated with a carbon precursor materialselected from a coal tar pitch, petroleum pitch, mesophase pitch,polymer, organic material, or a combination thereof so that the carbonprecursor material resides between surfaces of the solid electrodeactive material particles and the graphene sheets, and the methodfurther contains a step of heat-treating the graphene-embraced electrodeactive material to convert the carbon precursor material to a carbonmaterial and pores, wherein the pores form empty spaces between surfacesof the solid electrode active material particles and the graphenesheets, and the carbon material is coated on the surfaces of solidelectrode active material particles and/or chemically bonds the graphenesheets together.

In some embodiments, the particles of solid electrode active materialcontain particles pre-coated with a sacrificial material selected from ametal, pitch, polymer, organic material, or a combination thereof insuch a manner that the sacrificial material resides between surfaces ofparticles of solid electrode active material and the graphene sheets,and the method further contains a step of partially or completelyremoving the sacrificial material to form empty spaces between surfacesof the solid electrode active material particles and the graphenesheets.

In some embodiments, the method further comprises a step of exposing thegraphene-embraced electrode active material to a liquid or vapor of aconductive material that is conductive to electrons and/or ions oflithium, sodium, magnesium, aluminum, or zinc.

The particles of electrode active material may be an anode activematerial selected from the group consisting of: (A) lithiated andun-lithiated silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony(Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel(Ni), cobalt (Co), and cadmium (Cd); (B) lithiated and un-lithiatedalloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti,Ni, Co, or Cd with other elements; (C) lithiated and un-lithiatedoxides, carbides, nitrides, sulfides, phosphides, selenides, andtellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, or Cd, andtheir mixtures, composites, or lithium-containing composites; (D)lithiated and un-lithiated salts and hydroxides of Sn; (E) lithiumtitanate, lithium manganate, lithium aluminate, lithium-containingtitanium oxide, lithium transition metal oxide; and combinationsthereof.

The electrode active material may be a cathode active material selectedfrom an inorganic material, an organic or polymeric material, a metaloxide/phosphate/sulfide, or a combination thereof. The metaloxide/phosphate/sulfide may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,sodium cobalt oxide sodium nickel oxide, sodium manganese oxide, sodiumvanadium oxide, sodium-mixed metal oxide, sodium iron phosphate, sodiummanganese phosphate, sodium vanadium phosphate, sodium mixed metalphosphate, transition metal sulfide, lithium polysulfide, sodiumpolysulfide, magnesium polysulfide, or a combination thereof.

In some embodiments, the electrode active material may be a cathodeactive material selected from sulfur, sulfur compound, sulfur-carboncomposite, sulfur-polymer composite, lithium polysulfide, transitionmetal dichalcogenide, a transition metal trichalcogenide, or acombination thereof. The inorganic material may be selected from TiS₂,TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, a vanadium oxide, or acombination thereof.

The metal oxide/phosphate/sulfide contains a vanadium oxide selectedfrom the group consisting of VO₂, Li_(x)VO₂, V₂O₅, Li_(x)V₂O₅, V₃O₈,Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃, LiV₆O₁₃, their dopedversions, their derivatives, and combinations thereof, wherein 0.1<x<5.In some embodiments, the metal oxide/phosphate/sulfide is selected froma layered compound LiMO₂, spinel compound LiM₂O₄, olivine compoundLiMPO₄, silicate compound Li₂MSiO₄, Tavorite compound LiMPO₄F, boratecompound LiMBO₃, or a combination thereof, wherein M is a transitionmetal or a mixture of multiple transition metals.

The inorganic material may be selected from: (a) bismuth selenide orbismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof.

The organic material or polymeric material is selected fromPoly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, Quino(triazene), redox-active organic material,Tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,Hexaazatrinaphtylene (HATN), Hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-Benzylidene hydantoin, Isatine lithium salt, Pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity and rigidity so as to enable the peeling-off of graphenesheets from the graphitic material particles.

The thioether polymer in the above list may be selected fromPoly[methanetetryl-tetra(thiomethylene)] (PMTTM),Poly(2,4-dithiopentanylene) (PDTP), a polymer containingPoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, Poly(2-phenyl-1,3-dithiolane) (PPDT),Poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In some embodiments, the organic material contains a phthalocyaninecompound selected from copper phthalocyanine, zinc phthalocyanine, tinphthalocyanine, iron phthalocyanine, lead phthalocyanine, nickelphthalocyanine, vanadyl phthalocyanine, fluorochromium phthalocyanine,magnesium phthalocyanine, manganous phthalocyanine, dilithiumphthalocyanine, aluminum phthalocyanine chloride, cadmiumphthalocyanine, chlorogallium phthalocyanine, cobalt phthalocyanine,silver phthalocyanine, a metal-free phthalocyanine, a chemicalderivative thereof, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity and rigidity so as to enable the peeling-off of graphenesheets from the graphitic material particles.

In some embodiments, the electrode active material particles includepowder, flakes, beads, pellets, spheres, wires, fibers, filaments,discs, ribbons, or rods, having a diameter or thickness from 10 nm to 20μm. Preferably, the diameter or thickness is from 1 μm to 100 μm.

In the invented method, the graphitic material may be selected fromnatural graphite, synthetic graphite, highly oriented pyrolyticgraphite, graphite fiber, graphitic nanofiber, graphite fluoride,chemically modified graphite, mesocarbon micro-bead, partiallycrystalline graphite, or a combination thereof.

The method energy impacting apparatus may be a vibratory ball mill,planetary ball mill, high energy mill, basket mill, agitator ball mill,cryogenic ball mill, micro ball mill, tumbler ball mill, continuous ballmill, stirred ball mill, pressurized ball mill, plasma-assisted ballmill, freezer mill, vibratory sieve, bead mill, nano bead mill,ultrasonic homogenizer mill, centrifugal planetary mixer, vacuum ballmill, or resonant acoustic mixer. The procedure of operating the energyimpacting apparatus may be conducted in a continuous manner using acontinuous energy impacting device.

In the graphene-embraced electrode active material particles, thegraphene sheets contain single-layer graphene sheets. In someembodiments, the graphene sheets contain at least 80% single-layergraphene or at least 80% few-layer graphene having no greater than 10graphene planes.

The impacting chamber may further contain a functionalizing agent andstep (b) of operating the energy impacting apparatus acts to chemicallyfunctionalize said graphene sheets with said functionalizing agent. Thefunctionalizing agent may contain a chemical functional group selectedfrom alkyl or aryl silane, alkyl or aralkyl group, hydroxyl group,carboxyl group, amine group, sulfonate group (—SO₃H), aldehydic group,quinoidal, fluorocarbon, or a combination thereof.

In some embodiments, the functionalizing agent contains an oxygenatedgroup selected from the group consisting of hydroxyl, peroxide, ether,keto, and aldehyde. In some embodiments, the functionalizing agentcontains a functional group selected from the group consisting of SO₃H,COOH, NH₂, OH, R′CHOH, CHO, CN, COCl, halide, COSH, SH, COOR′, SR′,SiR′₃, Si(—OR′)_(y)R′₃-y, Si(—O—SiR′₂—)OR′, R″, Li, AlR′₂, Hg—X, TLZ₂and Mg—X; wherein y is an integer equal to or less than 3, R′ ishydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, orpoly(alkylether), R″ is fluoroalkyl, fluoroaryl, fluorocycloalkyl,fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate ortrifluoroacetate, and combinations thereof.

In some embodiments, the functionalizing agent contains a functionalgroup is selected from the group consisting of amidoamines, polyamides,aliphatic amines, modified aliphatic amines, cycloaliphatic amines,aromatic amines, anhydrides, ketimines, diethylenetriamine (DETA),triethylene-tetramine (TETA), tetraethylene-pentamine (TEPA),polyethylene polyamine, polyamine epoxy adduct, phenolic hardener,non-brominated curing agent, non-amine curatives, and combinationsthereof.

The functionalizing agent may contain a functional group selected fromOY, NHY, O═C—OY, P═C—NR′Y, O═C—SY, O═C—Y, —CR′1-OY, N′Y or C′Y, and Y isa functional group of a protein, a peptide, an amino acid, an enzyme, anantibody, a nucleotide, an oligonucleotide, an antigen, or an enzymesubstrate, enzyme inhibitor or the transition state analog of an enzymesubstrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN, R′X,R′N′(R′)₃X″, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—) OR′,R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′,(C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than200.

The present invention also provides a mass of graphene-embracedparticles of solid active material produced by the aforementionedmethod, wherein the graphene proportion is from 0.01% to 20% by weightbased on the total weight of graphene and solid active materialparticles combined.

Also provided is a battery electrode containing the graphene-embracedelectrode active material produced according to the presently inventedmethod, and a battery containing such an electrode. The batteryelectrode containing the graphene-embraced electrode active material maybe a lithium-ion battery, lithium metal secondary battery,lithium-sulfur battery, lithium-air battery, lithium-selenium battery,sodium-ion battery, sodium metal secondary battery, sodium-sulfurbattery, sodium-air battery, magnesium-ion battery, magnesium metalbattery, aluminum-ion battery, aluminum metal secondary battery,zinc-ion battery, zinc metal battery, or zinc-air battery.

It may be noted that the graphene production step per se (peeling offgraphene sheets directly from graphite particles and immediately orconcurrently transferring these graphene sheets to electrode activematerial particle surfaces) is quite surprising, considering the factthat prior researchers and manufacturers have focused on more complex,time intensive and costly methods to create graphene in industrialquantities. In other words, it has been generally believed that chemicalintercalation and oxidation is needed to produce bulk quantities ofisolated graphene sheets (NGPs). The present invention defies thisexpectation in many ways:

-   -   1. Unlike the chemical intercalation and oxidation (which        requires expansion of inter-graphene spaces, further expansion        or exfoliation of graphene planes, and full separation of        exfoliated graphene sheets), the instant method directly removes        graphene sheets from a source graphitic material and transfers        these graphene sheets to surfaces of electrode active material        particles. No undesirable chemicals (e.g. sulfuric acid and        nitric acid) are used.    -   2. Unlike oxidation and intercalation, pristine graphene sheets        can be transferred onto the electrode active material. The        sheets being free of oxidation damage allow the creation of        graphene-encapsulated particle products with higher electrical        and thermal conductivity.    -   3. Contrary to common production methods, a washing process        requiring substantial amounts of water or solvent is not needed    -   4. Unlike bottom up production methods capable of producing        small graphene sheets, large graphene sheets can be produced        with the instant method.    -   5. Unlike CVD and solution-based metalorganic production        methods, elevated temperatures are not required to reduce        graphene oxide to graphene and metalorganic compounds to pure        metal. This greatly reduces the opportunity for undesirable        diffusion of carbon into the electrode active material.    -   6. Unlike CVD and solution-based metalorganic production        methods, this process is amenable to almost any electrode active        material. The electrode active material does not need to be a        compatible “template” or catalyst, as is required for the CVD        process.    -   7. This method allows the creation of continuous,        interpenetrating three dimensional networks of graphene sheets.    -   8. The present invention is amenable to industrial scale        production in a continuous energy impact device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A flow chart showing the most commonly used prior art process ofproducing highly oxidized graphene sheets (or nano graphene platelets,NGPs) that entails tedious chemical oxidation/intercalation, rinsing,and high-temperature exfoliation procedures.

FIG. 2 A diagram showing the presently invented process for producinggraphene-embraced or encapsulated electrode active material particlesvia an energy impacting apparatus.

FIG. 3 A diagram showing the presently invented process for producinggraphene-embraced electrode active material particles via a continuousball mill.

FIG. 4 Charge-discharge cycling behaviors of 3 lithium cells featuringCo₃O₄ particle-based anodes: a) containing un-protected Co₃O₄ particles,b) reduced graphene oxide (RGO)-embraced Co₃O₄ particles (a prior artapproach), and c) graphene-encapsulated Co₃O₄ particles produced by theinstant impact transfer method.

FIG. 5 Charge-discharge cycling behaviors of 2 lithium cells featuringSnO₂ particle-based anodes: one containing un-protected SnO₂ particlesand the other containing graphene-encapsulated SnO₂ particles producedby the instant impact transfer method (stainless steel balls).

FIG. 6 Charge-discharge cycling behaviors of 3 lithium cells featuringmicron-scaled (3 μm) Si particle-based anodes: a) one cell containingun-protected Si particles, b) a second cell containing graphene-embracedSi particles produced by the indirect transfer method (with externallyadded milling media, ZrO₂ balls), and c) a third cell containinggraphene-encapsulated Si particles produced by the direct transfermethod (Si particles themselves being the graphene-peeling agent).

FIG. 7 Charge-discharge cycling behaviors of 2 lithium cells featuringlithium iron phosphate (LFP) particle-based cathodes: one containingun-protected LFO particles (mixed with 12% by weight carbon) and theother containing graphene-encapsulated carbon-added LFP particlesproduced by the instant impact transfer method (4% graphene+8% C).

FIG. 8 Charge-discharge cycling behaviors of 3 lithium cells featuringLiV₂O₅ nanorod-based cathodes: a) containing protected LiV₂O₅ nanorods(mixed with 10% by weight carbon black particles, b) graphene-embracedLiV₂O₅ nanorods produced by the impact transfer method using MoO₂ balls(approximately 5% graphene+7% C), and c) LiV₂O₅ nanorods protected by acarbon matrix.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Carbon materials can assume an essentially amorphous structure (glassycarbon), a highly organized crystal (graphite), or a whole range ofintermediate structures that are characterized in that variousproportions and sizes of graphite crystallites and defects are dispersedin an amorphous matrix. Typically, a graphite crystallite is composed ofa number of graphene sheets or basal planes that are bonded togetherthrough van der Waals forces in the c-axis direction, the directionperpendicular to the basal plane. These graphite crystallites aretypically micron- or nanometer-sized. The graphite crystallites aredispersed in or connected by crystal defects or an amorphous phase in agraphite particle, which can be a graphite flake, carbon/graphite fibersegment, carbon/graphite whisker, or carbon/graphite nanofiber. In otherwords, graphene planes (hexagonal lattice structure of carbon atoms)constitute a significant portion of a graphite particle.

One preferred specific embodiment of the present invention is a methodof peeling off graphene planes of carbon atoms (1-10 planes of atomsthat constitute single-layer or few-layer graphene sheets) that aredirectly transferred to surfaces of electrode active material particles.A graphene sheet or nano graphene platelet (NGP) is essentially composedof a sheet of graphene plane or multiple sheets of graphene planestacked and bonded together (typically, on an average, less than 10sheets per multi-layer platelet). Each graphene plane, also referred toas a graphene sheet or a hexagonal basal plane, comprises atwo-dimensional hexagonal structure of carbon atoms. Each platelet has alength and a width parallel to the graphite plane and a thicknessorthogonal to the graphite plane. By definition, the thickness of an NGPis 100 nanometers (nm) or smaller, with a single-sheet NGP being as thinas 0.34 nm. However, the NGPs produced with the instant methods aremostly single-layer graphene and some few-layer graphene sheets (<10layers). The length and width of a NGP are typically between 200 nm and20 μm, but could be longer or shorter, depending upon the sizes ofsource graphite material particles.

The present invention provides a strikingly simple, fast, scalable,environmentally benign, and cost-effective process that avoidsessentially all of the drawbacks associated with prior art processes ofproducing graphene sheets and obviates the need to execute a separate(additional) process to combine the produced graphene sheets andparticles of an electrode active material together to form a compositeor hybrid electrode active material.

As schematically illustrated in FIG. 2, one preferred embodiment of thismethod entails placing particles of a source graphitic material,particles of a solid electrode active material, and impacting balls(particles of ball-milling media) in an impacting chamber. Afterloading, the resulting mixture is exposed to impacting energy, which isaccomplished, for instance, by rotating the chamber to enable theimpacting of the milling balls against graphite particles. Theserepeated impacting events (occurring in high frequencies and highintensity) act to peel off graphene sheets from the surfaces ofgraphitic material particles and tentatively transferred to the surfacesof these impacting balls first. When the graphene-coated impacting ballssubsequently impinge upon the solid electrode active material particles,the graphene sheets are transferred to surfaces of the electrode activematerial particles to form graphene-coated active material particles.Typically, the entire particle is covered by graphene sheets (fullywrapped around, embraced or encapsulated). Subsequently, the externallyadded impacting balls (e.g. ball-milling media) are separated from thegraphene-embraced particles.

The non-polymeric particles of ball-milling media may contain millingballs selected from ceramic particles (e.g. ZrO₂ or non-ZrO₂-based metaloxide particles), metal particles, glass particles, or a combinationthereof.

In less than two hours (often less than 1 hour) of operating the directtransfer process, most of the constituent graphene sheets of sourcegraphite particles are peeled off, forming mostly single-layer grapheneand few-layer graphene (mostly less than 5 layers or 5 graphene planes).Following the transfer process (graphene sheets wrapped around activematerial particles), the residual graphite particles (if present) areseparated from the graphene-embraced (graphene-encapsulated) particlesusing a broad array of methods. Separation or classification ofgraphene-embraced (graphene-encapsulated) particles from residualgraphite particles (if any) can be readily accomplished based on theirdifferences in weight or density, particle sizes, magnetic properties,etc. The resulting graphene-embraced particles are already atwo-component material; i.e. they are already “mixed” and there is noneed to have a separate process of mixing isolated graphene sheets withelectrode active material particles.

In other words, production of graphene sheets and mixing of graphenesheets with an electrode active material are essentially accomplishedconcurrently in one operation. This is in stark contrast to thetraditional processes of producing graphene sheets first and thensubsequently mixing the graphene sheets with an active material.Traditional dry mixing typically does not result in homogeneous mixingor dispersion of two or multiple components. It is also challenging toproperly disperse nanomaterials in a solvent to form a battery slurrymass for coating on a current collector.

As shown in FIG. 1, the prior art chemical processes for producinggraphene sheets or platelets alone typically involve immersing graphitepowder in a mixture of concentrated sulfuric acid, nitric acid, and anoxidizer, such as potassium permanganate or sodium perchlorate, forminga reacting mass that requires typically 5-120 hours to complete thechemical intercalation/oxidation reaction. Once the reaction iscompleted, the slurry is subjected to repeated steps of rinsing andwashing with water and then subjected to drying treatments to removewater. The dried powder, referred to as graphite intercalation compound(GIC) or graphite oxide (GO), is then subjected to a thermal shocktreatment. This can be accomplished by placing GIC in a furnace pre-setat a temperature of typically 800-1100° C. (more typically 950-1050°C.). The resulting products are typically highly oxidized graphene (i.e.graphene oxide with a high oxygen content), which must be chemically orthermal reduced to obtain reduced graphene oxide (RGO). RGO is found tocontain a high defect population and, hence, is not as conducting aspristine graphene. We have observed that that the pristine graphenepaper (prepared by vacuum-assisted filtration of pristine graphenesheets, as herein prepared) exhibit electrical conductivity values inthe range of 1,500-4,500 S/cm. In contrast, the RGO paper prepared bythe same paper-making procedure typically exhibits electricalconductivity values in the range of 100-1,000 S/cm.

In the most common implementation of prior art ball mill mixing,previously produced graphene sheets or platelets are added to electrodeactive material powders. Impact energy is applied via ball mill for aperiod of time to disperse graphene platelets or sheets in the powder.This is often carried out in a liquid (solvent) solution. Thedisadvantages of this graphene/active material mixing process areobvious—previously made graphene is a costly input material, solventrecovery is required, and most significantly, the graphene input intothe process has been damaged by oxidation during prior processing. Thisreduces desirable end properties, such as thermal conductivity andelectrical conductivity.

Another prior art process is coating of CVD onto metal nanoparticles.This is the most limited of all prior art methods, being possible onlyon certain metals that are suitable catalysts for facilitatingdecomposition of hydrocarbon gas to form carbon atoms and as templatesfor graphene to grow on. As a “bottom up” graphene production method, itrequires costly capital equipment and costly input materials.

In all these prior art processes for producing graphene-coated electrodeactive material particles, isolated graphene sheets and particles of theactive material are dispersed in a solvent (e.g. NMP) to form a slurry.The slurry is then dried (e.g. using spray drying) to formgraphene-active material composite particles. These composites do notnecessarily have the morphology or structure of active materialparticles being fully wrapped around or embraced.

In contrast, the presently invented impacting process entails combininggraphene production, functionalization (if desired), and mixing ofgraphene with electrode active material particles in a single operation.This fast and environmentally benign process not only avoids significantchemical usage, but also produces embracing graphene sheets of higherquality—pristine graphene as opposed to thermally reduced graphene oxideproduced by the prior art process. Pristine graphene enables thecreation of embraced particles with higher electrical and thermalconductivity.

Although the mechanisms remain incompletely understood, thisrevolutionary process of the present invention has essentiallyeliminated the conventionally required functions of graphene planeexpansion, intercalant penetration, exfoliation, and separation ofgraphene sheets and replace it with a single, entirely mechanicalpeeling process. The whole process can take less than 2 hours (typically10 minutes to 1 hour), and can be done with no added chemicals. This isabsolutely stunning, a shocking surprise to even those top scientistsand engineers or those of extraordinary ability in the art.

Another surprising result of the present study is the observation that awide variety of carbonaceous and graphitic materials can be directlyprocessed without any particle size reduction or pre-treatment. Theparticle size of graphite can be smaller than, comparable to, or largerthan the particle size of the electrode active material. The graphiticmaterial may be selected from natural graphite, synthetic graphite,highly oriented pyrolytic graphite, mesocarbon micro-bead, graphitefiber, graphitic nanofiber, graphite oxide, graphite fluoride,chemically modified graphite, exfoliated graphite, or a combinationthereof. It may be noted that the graphitic material used for the priorart chemical production and reduction of graphene oxide requires sizereduction to 75 um or less in average particle size. This processrequires size reduction equipment (for example hammer mills or screeningmills), energy input, and dust mitigation. By contrast, the energyimpacting device method can accept almost any size of graphiticmaterial. A starting graphitic material of several mm or cm in size orlarger or a starting material as small as nanoscaled has beensuccessfully processed to create graphene-coated or graphene-embeddedparticles of cathode or anode active materials. The only size limitationis the chamber capacity of the energy impacting device; but this chambercan be very large (industry-scaled).

The presently invented process is capable of producing single-layergraphene sheets that completely wrap around the particles of anelectrode active material. In many examples, the graphene sheetsproduced contain at least 80% single-layer graphene sheets. The grapheneproduced can contain pristine graphene, oxidized graphene with less than5% oxygen content by weight, graphene fluoride, graphene oxide with lessthan 5% fluorine by weight, graphene with a carbon content of no lessthan 95% by weight, or functionalized graphene.

The presently invented process does not involve the production of GICand, hence, does not require the exfoliation of GIC at a highexfoliation temperature (e.g. 800-1,100° C.). This is another majoradvantage from environmental protection perspective. The prior artprocesses require the preparation of dried GICs containing sulfuric acidand nitric acid intentionally implemented in the inter-graphene spacesand, hence, necessarily involve the decomposition of H₂SO₄ and HNO₃ toproduce volatile gases (e.g. NO_(x) and SO_(x)) that are highlyregulated environmental hazards. The presently invented processcompletely obviates the need to decompose H₂SO₄ and HNO₃ and, hence, isenvironmentally benign. No undesirable gases are released into theatmosphere during the combined graphite expansion/exfoliation/separationprocess of the present invention.

In a desired embodiment, the presently invented method is carried out inan automated and/or continuous manner. For instance, as illustrated inFIG. 3, the mixture of graphite particles 1 and electrode activematerial particles 2 (along with non-polymeric milling balls) isdelivered by a conveyer belt 3 and fed into a continuous ball mill 4.After ball milling to form graphene-embraced particles, the productmixture (possibly also containing some residual graphite particles) isdischarged from the ball mill apparatus 4 into a screening device (e.g.a rotary drum 5) to separate graphene-embraced particles from residualgraphite particles (if any). The graphene-embraced particles may bedelivered into a powder classifier, a cyclone, and or an electrostaticseparator. The particles may be further processed, if so desired, bymelting 7, pressing 8, or grinding/pelletizing apparatus 9. Theseprocedures can be fully automated. The process may includecharacterization or classification of the output material and recyclingof insufficiently processed material into the continuous energyimpacting device. The process may include weight monitoring of the loadin the continuous energy impacting device to optimize materialproperties and throughput.

The separation of the milling balls from the final products may beassisted by a magnetic separator 6 if the milling balls areferromagnetic (e.g. containing Fe, Co, Ni, or Mn-based metal in somedesired electronic configuration).

The electrode active materials that are placed into the impactingchamber can be an anode active material or a cathode active material.For the anode active materials, those materials capable of storinglithium ions greater than 372 mAh/g (theoretical capacity of naturalgraphite) are particularly desirable. Examples of these high-capacityanode active materials are Si, Ge, Sn, SnO₂, Co₃O₄, etc. As discussedearlier, these materials, if implemented in the anode, have the tendencyto expand and contract when the battery is charged and discharged. Atthe electrode level, the expansion and contraction of the anode activematerial can lead to expansion and contraction of the anode, causingmechanical instability of the battery cell. At the anode active materiallevel, repeated expansion/contraction of particles of Si, Ge, Sn, SnO₂,Co₃O₄, etc. quickly leads to pulverization of these particles and rapidcapacity decay of the electrode.

Thus, for the purpose of addressing these problems, the particles ofsolid electrode active material may contain prelithiated or pre-sodiatedparticles. In other words, before the electrode active materialparticles (such as Si, Ge, Sn, SnO₂, Co₃O₄, etc.) are embraced bygraphene sheets, these particles have already been previouslyintercalated with Li or Na ions (e.g. via electrochemical charging).This is a highly innovative and unique approach based on the followingconsiderations. The intercalation of these particles with Li or Na wouldallow these particles to expand to a large volume or to its fullcapacity (potentially up to 380% of its original volume). If theseprelithiated or pre-sodiated particles are then wrapped around or fullyembraced by graphene sheets and incorporated into an electrode (e.g.anode containing graphene-embraced Si or SnO₂ particles), the electrodewould no longer have any issues of electrode expansion andexpansion-induced failure during subsequent charge-discharge cycles ofthe lithium- or sodium-ion battery. In other words, the Si or SnO₂particles have been expanded to their maximum volume (during batterycharging) and they can only shrink (during subsequent batterydischarge). These contracted particles have been previously providedwith expansion space between these particles and the embracing graphenesheets. Our experimental data have shown that this strategy surprisinglyleads to significantly longer battery cycle life and better utilizationof the electrode active material capacity.

In some embodiments, prior to the instant graphene production, impacttransfer and embracing process, the particles of solid electrode activematerial contain particles that are pre-coated with a coating of aconductive material selected from carbon, pitch, carbonized resin, aconductive polymer, a conductive organic material, a metal coating, ametal oxide shell, or a combination thereof. The coating layer thicknessis preferably in the range from 1 nm to 10 μm, preferably from 10 nm to1 μm, and further preferably from 20 nm to 200 nm. This coating isimplemented for the purpose of establishing a solid-electrolyteinterface (SEI) to increase the useful cycle life of a lithium-ion orsodium-ion battery.

In some embodiments, the particles of solid electrode active materialcontain particles that are pre-coated with a carbon precursor materialselected from a coal tar pitch, petroleum pitch, mesophase pitch,polymer, organic material, or a combination thereof so that the carbonprecursor material resides between surfaces of the solid electrodeactive material particles and the graphene sheets, and the methodfurther contains a step of heat-treating the graphene-embraced electrodeactive material to convert the carbon precursor material to a carbonmaterial and pores, wherein the pores form empty spaces between surfacesof the solid electrode active material particles and the graphene sheetsand the carbon material is coated on the surfaces of solid electrodeactive material particles and/or chemically bonds the graphene sheetstogether. The carbon material helps to completely seal off the embracinggraphene sheets to prevent direct contact of the embraced anode activematerial with liquid electrolyte, which otherwise continues to formadditional SEI via continuously consuming the lithium ions or solvent inthe electrolyte, leading to rapid capacity decay.

In some embodiments, the particles of solid electrode active materialcontain particles pre-coated with a sacrificial material selected from ametal, pitch, polymer, organic material, or a combination thereof insuch a manner that the sacrificial material resides between surfaces ofsolid electrode active material particles and the graphene sheets, andthe method further contains a step of partially or completely removingthe sacrificial material to form empty spaces between surfaces of thesolid electrode active material particles and the graphene sheets. Theempty spaces can accommodate the expansion of embraced active materialparticles without breaking the embraced particles.

In some embodiments, the method further comprises a step of exposing thegraphene-embraced electrode active material to a liquid or vapor of aconductive material that is conductive to electrons and/or ions oflithium, sodium, magnesium, aluminum, or zinc. This procedure serves toprovide a stable SEI or to make the SEI more stable.

The particles of electrode active material may be an anode activematerial selected from the group consisting of: (A) lithiated andun-lithiated silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony(Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel(Ni), cobalt (Co), and cadmium (Cd); (B) lithiated and un-lithiatedalloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti,Ni, Co, or Cd with other elements; (C) lithiated and un-lithiatedoxides, carbides, nitrides, sulfides, phosphides, selenides, andtellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, or Cd, andtheir mixtures, composites, or lithium-containing composites; (D)lithiated and un-lithiated salts and hydroxides of Sn; (E) lithiumtitanate, lithium manganate, lithium aluminate, lithium-containingtitanium oxide, lithium transition metal oxide; and combinationsthereof. Both sodiated and un-sodiated versions of the materials in theabove list are also anode active materials for sodium-ion batteries.

The electrode active material may be a cathode active material selectedfrom an inorganic material, an organic material, an intrinsicallyconducting polymer (known to be capable of string lithium ions), a metaloxide/phosphate/sulfide, or a combination thereof. The metaloxide/phosphate/sulfide may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,sodium cobalt oxide sodium nickel oxide, sodium manganese oxide, sodiumvanadium oxide, sodium-mixed metal oxide, sodium iron phosphate, sodiummanganese phosphate, sodium vanadium phosphate, sodium mixed metalphosphate, transition metal sulfide, lithium polysulfide, sodiumpolysulfide, magnesium polysulfide, or a combination thereof.

In some embodiments, the electrode active material may be a cathodeactive material selected from sulfur, sulfur compound, sulfur-carboncomposite, sulfur-polymer composite, lithium polysulfide, transitionmetal dichalcogenide, a transition metal trichalcogenide, or acombination thereof. The inorganic material may be selected from TiS₂,TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, a vanadium oxide, or acombination thereof. This group of materials is particularly suitablefor use as a cathode active material of a lithium metal battery.

The metal oxide/phosphate/sulfide contains a vanadium oxide selectedfrom the group consisting of VO₂, Li_(x)VO₂, V₂O₅, Li_(x)V₂O₅, V₃O₅,Li_(x)V₃O₅, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃, Li_(x)V₆O₁₃, theirdoped versions, their derivatives, and combinations thereof, wherein0.1<x<5. In some embodiments, the metal oxide/phosphate/sulfide isselected from a layered compound LiMO₂, spinel compound LiM₂O₄, olivinecompound LiMPO₄, silicate compound Li₂MSiO₄, Tavorite compound LiMPO₄F,borate compound LiMBO₃, or a combination thereof, wherein M is atransition metal or a mixture of multiple transition metals.

The inorganic material may be selected from: (a) bismuth selenide orbismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof.

The organic material or polymeric material may be selected fromPoly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, Quino(triazene), redox-active organic material,Tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,Hexaazatrinaphtylene (HATN), Hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-Benzylidene hydantoin, Isatine lithium salt, Pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity, rigidity and strength so as to enable the peeling-off ofgraphene sheets from the graphitic material particles.

The thioether polymer in the above list may be selected fromPoly[methanetetryl-tetra(thiomethylene)](PMTTM),Poly(2,4-dithiopentanylene) (PDTP), a polymer containingPoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, Poly(2-phenyl-1,3-dithiolane) (PPDT),Poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).

In some embodiments, the organic material contains a phthalocyaninecompound selected from copper phthalocyanine, zinc phthalocyanine, tinphthalocyanine, iron phthalocyanine, lead phthalocyanine, nickelphthalocyanine, vanadyl phthalocyanine, fluorochromium phthalocyanine,magnesium phthalocyanine, manganous phthalocyanine, dilithiumphthalocyanine, aluminum phthalocyanine chloride, cadmiumphthalocyanine, chlorogallium phthalocyanine, cobalt phthalocyanine,silver phthalocyanine, a metal-free phthalocyanine, a chemicalderivative thereof, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity and rigidity so as to enable the peeling-off of graphenesheets from the graphitic material particles.

In some embodiments, the electrode active material particles includepowder, flakes, beads, pellets, spheres, wires, fibers, filaments,discs, ribbons, or rods, having a diameter or thickness from 10 nm to 20μm. Preferably, the diameter or thickness is from 1 μm to 100 μm.

In the invented method, the graphitic material may be selected fromnatural graphite, synthetic graphite, highly oriented pyrolyticgraphite, graphite fiber, graphitic nanofiber, graphite fluoride,chemically modified graphite, mesocarbon micro-bead, partiallycrystalline graphite, or a combination thereof.

The energy impacting apparatus may be a vibratory ball mill, planetaryball mill, high energy mill, basket mill, agitator ball mill, cryogenicball mill, micro ball mill, tumbler ball mill, continuous ball mill,stirred ball mill, pressurized ball mill, plasma-assisted ball mill,freezer mill, vibratory sieve, bead mill, nano bead mill, ultrasonichomogenizer mill, centrifugal planetary mixer, vacuum ball mill, orresonant acoustic mixer. The procedure of operating the energy impactingapparatus may be conducted in a continuous manner using a continuousenergy impacting device

Graphene sheets transferred to electrode active material surfaces have asignificant proportion of surfaces that correspond to the edge planes ofgraphite crystals. The carbon atoms at the edge planes are reactive andmust contain some heteroatom or group to satisfy carbon valency. Thereare many types of functional groups (e.g. hydroxyl and carboxylic) thatare naturally present at the edge or surface of graphene nanoplateletsproduced through transfer to a solid carrier particle. Theimpact-induced kinetic energy is of sufficient energy and intensity tochemically activate the edges and even surfaces of graphene sheetsembraced around active material particles (e.g. creating highly activesites or free radicals). Provided that certain chemical speciescontaining desired chemical function groups (e.g. OH—, —COOH, —NH₂, Br—,etc.) are included in the impacting chamber, these functional groups canbe imparted to graphene edges and/or surfaces. In other words,production and chemical functionalization of graphene sheets can beaccomplished concurrently by including appropriate chemical compounds inthe impacting chamber. In summary, a major advantage of the presentinvention over other processes is the simplicity of simultaneousproduction and modification of graphene surface chemistry for improvedbattery performance.

Graphene sheets derived by this process may be functionalized throughthe inclusion of various chemical species in the impacting chamber. Ineach group of chemical species discussed below, we selected 2 or 3chemical species for functionalization studies.

In one preferred group of chemical agents, the resulting functionalizedNGP may broadly have the following formula (e): [NGP]—R_(m), wherein mis the number of different functional group types (typically between 1and 5), R is selected from SO₃H, COOH, NH₂, OH, R′CHOH, CHO, CN, COCl,halide, COSH, SH, COOR′, SR′, SiR′₃, Si(—OR′—)_(y)R′₃-y,Si(—O—SiR′₂—)OR′, R″, Li, AlR′₂, Hg—X, TlZ₂ and Mg—X; wherein y is aninteger equal to or less than 3, R′ is hydrogen, alkyl, aryl,cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R″ isfluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, Xis halide, and Z is carboxylate or trifluoroacetate.

Graphene-embraced electrode active material particles may be used toimprove the mechanical properties, electrical conductivity and thermalconductivity of an electrode. For enhanced lithium-capturing and storingcapability, the functional group —NH₂ and —OH are of particularinterest. For example, diethylenetriamine (DETA) has three —NH₂ groups.If DETA is included in the impacting chamber, one of the three —NH₂groups may be bonded to the edge or surface of a graphene sheet and theremaining two un-reacted —NH₂ groups will be available for reversiblycapturing a lithium or sodium atom and forming a redox pair therewith.Such an arrangement provides an additional mechanism for storing lithiumor sodium ions in a battery electrode.

Other useful chemical functional groups or reactive molecules may beselected from the group consisting of amidoamines, polyamides, aliphaticamines, modified aliphatic amines, cycloaliphatic amines, aromaticamines, anhydrides, ketimines, diethylenetriamine (DETA),triethylene-tetramine (TETA), tetraethylene-pentamine (TEPA),hexamethylenetetramine, polyethylene polyamine, polyamine epoxy adduct,phenolic hardener, non-brominated curing agent, non-amine curatives, andcombinations thereof. These functional groups are multi-functional, withthe capability of reacting with at least two chemical species from atleast two ends. Most importantly, they are capable of bonding to theedge or surface of graphene using one of their ends and, duringsubsequent epoxy curing stage, are able to react with epoxide or epoxyresin material at one or two other ends.

The above-described [NGP]—R_(m) may be further functionalized. This canbe conducted by opening up the lid of an impacting chamber after the—R_(m) groups have been attached to graphene sheets and then adding thenew functionalizing agents to the impacting chamber and resuming theimpacting operation. The resulting graphene sheets or platelets includecompositions of the formula: [NGP]-A_(m), where A is selected from OY,NHY, O═C—OY, P—C—NR′Y, O═C—SY, O═C—Y, —CR′1-OY, N′Y or C′Y, and Y is anappropriate functional group of a protein, a peptide, an amino acid, anenzyme, an antibody, a nucleotide, an oligonucleotide, an antigen, or anenzyme substrate, enzyme inhibitor or the transition state analog of anenzyme substrate or is selected from R′—OH, R′—NR′₂, R′SH, R′CHO, R′CN,R′X, R′N(R′)₃X″, R′SiR′₃, R′Si(—OR′—)_(y)R′_(3-y), R′Si(—O—SiR′₂—)OR′,R′—R″, R′—N—CO, (C₂H₄O—)_(w)H, (—C₃H₆O—)_(w)H, (—C₂H₄O)_(w)—R′,(C₃H₆O)_(w)—R′, R′, and w is an integer greater than one and less than200.

The NGPs may also be functionalized to produce compositions having theformula: [NGP]—[R′-A]_(m), where m, R′ and A are as defined above. Thecompositions of the invention also include NGPs upon which certaincyclic compounds are adsorbed. These include compositions of matter ofthe formula: [NGP]—[X—R_(a)]_(m), where a is zero or a number less than10, X is a polynuclear aromatic, polyheteronuclear aromatic ormetallopolyheteronuclear aromatic moiety and R is as defined above.Preferred cyclic compounds are planar. More preferred cyclic compoundsfor adsorption are porphyrins and phthalocyanines. The adsorbed cycliccompounds may be functionalized. Such compositions include compounds ofthe formula, [NGP]—[X-A_(a)]_(m), where m, a, X and A are as definedabove.

The functionalized NGPs of the instant invention can be prepared bysulfonation, electrophilic addition to deoxygenated platelet surfaces,or metallation. The graphitic platelets can be processed prior to beingcontacted with a functionalizing agent. Such processing may includedispersing the platelets in a solvent. In some instances the plateletsmay then be filtered and dried prior to contact. One particularly usefultype of functional group is the carboxylic acid moieties, whichnaturally exist on the surfaces of NGPs if they are prepared from theacid intercalation route discussed earlier. If carboxylic acidfunctionalization is needed, the NGPs may be subjected to chlorate,nitric acid, or ammonium persulfate oxidation.

Carboxylic acid functionalized graphitic platelets are particularlyuseful because they can serve as the starting point for preparing othertypes of functionalized NGPs. For example, alcohols or amides can beeasily linked to the acid to give stable esters or amides. If thealcohol or amine is part of a di- or poly-functional molecule, thenlinkage through the O- or NH-leaves the other functionalities as pendantgroups. These reactions can be carried out using any of the methodsdeveloped for esterifying or aminating carboxylic acids with alcohols oramines as known in the art. Examples of these methods can be found in G.W. Anderson, et al., J. Amer. Chem. Soc. 96, 1839 (1965), which ishereby incorporated by reference in its entirety. Amino groups can beintroduced directly onto graphitic platelets by treating the plateletswith nitric acid and sulfuric acid to obtain nitrated platelets, thenchemically reducing the nitrated form with a reducing agent, such assodium dithionite, to obtain amino-functionalized platelets.Functionalization of the graphene-coated inorganic particles may be usedas a method to introduce dopants into the electrode active material.

The following examples serve to provide the best modes of practice forthe present invention and should not be construed as limiting the scopeof the invention:

Example 1: Graphene Embraced Particles of Electrode Active Materials

Several types of electrode active materials (both anode and cathodeactive materials) in a fine powder form were investigated. These includeCo₃O₄, Si, LiCoO₂, LiMn₂O₄, lithium iron phosphate, etc., which are usedas examples to illustrate the best mode of practice. These activematerials were either prepared in house or purchased from commercialsources.

In a typical experiment, 1 kg of electrode active material powder and100 grams of natural flake graphite, 50 mesh (average particle size 0.18mm; Asbury Carbons, Asbury N.J.), and milling balls (stainless steelballs, ZrO₂ balls, glass balls, and MoO₂ balls, etc.) were placed in ahigh-energy ball mill container. The ball mill was operated at 300 rpmfor 0.5 to 4 hours. The container lid was then removed and particles ofthe active materials were found to be fully coated (embraced orencapsulated) with a dark layer, which was verified to be graphene byRaman spectroscopy. The mass of processed material was placed over a 50mesh sieve and, in some cases, a small amount of unprocessed flakegraphite was removed.

Example 2: Functionalized Graphene-Encapsulated Sn Particles

The process of example 1 was replicated with the inclusion of 50 gramsof urea as a nitrogen source. The coated powder created wasfunctionalized graphene-encapsulated Sn particles for use as an anodeactive material in a lithium-ion battery. It may be noted that chemicalfunctionalization is used to improve wettability of the electrode activematerial by the electrolyte or the compatibility between the electrodeactive material and the electrolyte in a battery.

Example 3: Graphene-Embraced SnO₂ Particles

In an experiment, 2 grams of 99.9% purity tin oxide powder (90 nmdiameter), 0.25 grams highly oriented pyrolytic graphite (HOPG), and 1gram of ZrO₂ balls were placed in a resonant acoustic mill and processedfor 5 minutes. For comparison, the same experiment was conducted, butwithout the presence of zirconia milling beads. The direct transferprocess (tin oxide particles serving as the milling media per se withoutthe externally added zirconia milling beads) led to mostlysingle-particle particulate (each particulate contains one particleencapsulated by graphene sheets). In contrast, with the presence ofexternally added milling beads, a graphene-embraced particulate tends tocontain some multiple tin oxide particles (typically 3-50) wrappedaround by graphene sheets. These same results were also observed formost of metal oxide-based electrode active materials (both anode andcathode).

Example 4: Graphene-Encapsulated Si Micron Particles

In a first experiment, 500 g of Si powder (particle diameter ˜3 μm), 50grams of highly oriented pyrolytic graphite (HOPG), and 100 grams ofZrO₂ balls were placed in a high-intensity ball mill. The mill wasoperated for 20 minutes, after which the container lid was opened andun-processed HOPG was removed by a 50 mesh sieve. The Si powder wascoated with a dark layer, which was verified to be graphene by Ramanspectroscopy.

In a second experiment, micron-scaled Si particles from the same batchwere pre-coated with a layer of polyethylene (PE) using amicro-encapsulation method that includes preparing solution of PEdissolved in toluene, dispersing Si particles in this solution to form aslurry, and spry-drying the slurry to form PE-encapsulated Si particles.Then, 500 g of PE-encapsulated Si particles and 50 grams of HOPG wereplaced in a high-intensity ball mill. The mill was operated for 20minutes, after which the container lid was opened and un-processed HOPGwas removed by a 50 mesh sieve. The PE-encapsulated Si particles (PElayer varied from 0.3 to 2.0 μm) were now also embraced with graphenesheets. These graphene-embraced PE-encapsulated particles were thensubjected to a heat treatment (up to 600° C.) that converted PE tocarbon. The converted carbon was mostly deposited on the exteriorsurface of the Si particles, leaving behind a gap or pores between theSi particle surface and the encapsulating graphene shell. This gapprovides room to accommodate the volume expansion of the Si particlewhen the lithium-ion battery is charged. Such a strategy leads tosignificantly improved battery cycle life.

In a third experiment, the Si particles were subjected toelectrochemical prelithiation to prepare several samples containing from5% to 54% Li. Prelithiation of an electrode active material means thematerial is intercalated or loaded with lithium before a battery cell ismade. Various prelithiated Si particles were then subjected to thepresently invented graphene encapsulation treatment. The resultinggraphene-encapsulated prelithiated Si particles were incorporated as ananode active material in several lithium-ion cells.

Example 5: Graphene-Embraced Ge Particles (Using Mesocarbon Micro Beadsor MCMBs as the Graphene Source)

In one example, 500 grams of B-doped Ge powder (anode active material)and 10 grams of MCMBs (China Steel Chemical Co., Taiwan) were placed ina ball mill (with or without milling balls), and processed for 3 hours.In separate experiments, un-processed MCMB was removed by sieving, airclassification, and settling in a solvent solution. The graphene loadingof the coated particles was estimated to be 1.4 weight %.

Example 6: Graphene Encapsulation Via Indirect Direct Transfer Vs.Chemical Production of Graphene Sheets Plus Freezer Milling

A sample of graphene-embraced lithium titanate particles was preparedvia the presently invented indirect transfer method (using siliconcarbide balls as the milling media and natural graphite as the graphenesource).

In a separate experiment, 10 grams of lithium titanate powder and 1 gramof reduced graphene oxide sheets (produced with the Hummer's methodexplained below) were placed in a freezer mill (Spex Mill, Spex SamplePrep, Metuchen N.J.) and processed for 10 minutes. In this experiment,graphite oxide as prepared by oxidation of graphite flakes with sulfuricacid, nitrate, and permanganate according to the method of Hummers [U.S.Pat. No. 2,798,878, Jul. 9, 1957]. Upon completion of the reaction, themixture was poured into deionized water and filtered. The graphite oxidewas repeatedly washed in a 5% solution of HCl to remove the majority ofthe sulfate ions. The sample was then washed repeatedly with deionizedwater until the pH of the filtrate was neutral. The slurry wasspray-dried and placed in a vacuum oven at 60° C. for 24 hours. Theinterlayer spacing of the resulting laminar graphite oxide wasdetermined by the Debey-Scherrer X-ray technique to be approximately0.73 nm (7.3 A). A sample of this material was subsequently transferredto a furnace pre-set at 650° C. for 4 minutes for exfoliation and heatedin an inert atmosphere furnace at 1200° C. for 4 hours to create a lowdensity powder comprised of few-layer reduced graphene oxide (RGO).Surface area was measured via nitrogen adsorption BET.

As discussed in the Background section, there are seven (7) majorproblems associated with the chemical method of graphene production. Inaddition, the graphene sheets, once produced, tend to result in theformation of multiple-particle particulates that each contains aplurality of electrode active material particles embraced orencapsulated by graphene sheets. They appear to be incapable ofencapsulating a single particle.

Example 7: Graphene-Encapsulated Lithium Iron Phosphate (LFP) as aCathode Active Material for a Lithium Metal Battery

LFP powder, un-coated or carbon-coated, is commercially available fromseveral sources. The carbon-coated LFP powder and un-coated LFP powdersamples were separately mixed with natural graphite particles in ballmill pots of a high-intensity ball mill apparatus. The apparatus wasoperated for 0.5 to 4 hours for each LFP material to producegraphene-encapsulated LFP particles. Zirconia beads were added asmilling media in the ball milling apparatus.

Example 8: Graphene-Encapsulated V₂O₅ as an Example of a TransitionMetal Oxide Cathode Active Material of a Lithium Battery

V₂O₅ powder is commercially available. A mixture of V₂O₅ powder andnatural graphite (10/1 weight ratio) was sealed in each of 4 ballmilling pots symmetrically positioned in a high-intensity ball millcontaining MoO₂ balls as the milling media. The mill was operated for 1hour to produce particulates of graphene-encapsulated V₂O₅ particles,which were implemented as the cathode active material in a lithium metalbattery.

Example 9: LiCoO₂ as an Example of Lithium Transition Metal OxideCathode Active Material for a Lithium-Ion Battery

In a set of experiments, a mixture of LiCoO₂ powder and natural graphite(100/1-10/1 weight ratio) was sealed in each of 4 ball milling potssymmetrically positioned in a high-intensity ball mill containing ZrO₂balls as the milling media. The mill was operated for 0.5-4 hours toproduce particulates of graphene-encapsulated LiCoO₂ particles.

Example 10: Organic Material (Li₂C₆O₆) as a Cathode Active Material of aLithium Metal Battery

The experiments associated with this example were conducted to determineif organic materials, such as Li₂C₆O₆, can be encapsulated in graphenesheets using the presently invented impact transfer method. The resultis that organic active materials alone (without particles of aninorganic material) are typically incapable of peeling off graphenesheets from graphite particles. Preferably, rigid milling balls (e.g.ZrO₂) are larger than 50 μm to prevent the balls from being packed withthe organic active material into graphene-wrapped particles.

In order to synthesize dilithium rhodizonate (Li₂C₆O₆), the rhodizonicacid dihydrate (species 1 in the following scheme) was used as aprecursor. A basic lithium salt, Li₂CO₃ can be used in aqueous media toneutralize both enediolic acid functions. Strictly stoichiometricquantities of both reactants, rhodizonic acid and lithium carbonate,were allowed to react for 10 hours to achieve a yield of 90%. Dilithiumrhodizonate (species 2) was readily soluble even in a small amount ofwater, implying that water molecules are present in species 2. Water wasremoved in a vacuum at 180° C. for 3 hours to obtain the anhydrousversion (species 3).

A mixture of an organic cathode active material (Li₂C₆O₆) and aninorganic cathode active material (V₂O₅ and MoS₂, separately) wasball-milled for 0.5-2.0 hours to obtain a mixture ofgraphene-encapsulated particles.

It may be noted that the two Li atoms in the formula Li₂C₆O₆ are part ofthe fixed structure and they do not participate in reversible lithiumion storing and releasing. This implies that lithium ions must come fromthe anode side. Hence, there must be a lithium source (e.g. lithiummetal or lithium metal alloy) at the anode. In one battery cell hereintested, the anode current collector (Cu foil) is deposited with a layerof lithium (via sputtering). The resulting cell is a lithium metal cell.

Example 11: Graphene-Encapsulated Na₃V₂(PO₄)₃/C and Na₃V₂(PO₄)₃ Cathodesfor Sodium Metal Batteries

The Na₃V₂(PO₄)₃/C sample was synthesized by a solid state reactionaccording to the following procedure: a stoichiometric mixture ofNaH₂PO₄.2H₂O (99.9%, Alpha) and V₂O₃ (99.9%, Alpha) powders was put inan agate jar as a precursor and then the precursor was ball-milled in aplanetary ball mill at 400 rpm in a stainless steel vessel for 8 h.During ball milling, for the carbon coated sample, sugar (99.9%, Alpha)was also added as the carbon precursor and the reductive agent, whichprevents the oxidation of V3⁺. After ball milling, the mixture washeated at 900° C. for 24 h in Ar atmosphere. Separately, the Na₃V₂(PO₄)₃powder was prepared in a similar manner, but without sugar. Samples ofboth powders were then subjected to ball milling in the presence ofnatural graphite particles to prepare graphene-encapsulated Na₃V₂(PO₄)₃particles and graphene-encapsulated carbon-coated Na₃V₂(PO₄)₃ particles.The cathode active materials were used in several Na metal cellscontaining 1 M of NaPF₆ salt in PC+DOL as the electrolyte. It wasdiscovered that graphene encapsulation significantly improved the cyclestability of all Na metal cells studied. In terms of cycle life, thefollowing sequence was observed: graphene-encapsulatedNa₃V₂(PO₄)₃/C>graphene-encapsulatedNa₃V₂(PO₄)₃>Na₃V₂(PO₄)₃/C>Na₃V₂(PO₄)₃.

Example 12: Preparation of Graphene-Encapsulated MoS₂ Particles as aCathode Active Material of a Na Metal Battery

A wide variety of inorganic materials were investigated in this example.For instance, an ultra-thin MoS₂ material was synthesized by a one-stepsolvothermal reaction of (NH₄)₂MoS₄ and hydrazine inN,N-dimethylformamide (DMF) at 200° C. In a typical procedure, 22 mg of(NH₄)₂MoS₄ was added to 10 ml of DMF. The mixture was sonicated at roomtemperature for approximately 10 min until a clear and homogeneoussolution was obtained. After that, 0.1 ml of N₂H₄.H₂O was added. Thereaction solution was further sonicated for 30 min before beingtransferred to a 40 mL Teflon-lined autoclave. The system was heated inan oven at 200° C. for 10 h. Product was collected by centrifugation at8000 rpm for 5 min, washed with DI water and recollected bycentrifugation. The washing step was repeated for 5 times to ensure thatmost DMF was removed. Finally, MoS₂ particles were dried and subjectedto graphene encapsulation by high-intensity ball milling (with MoO₂balls) in the presence of natural graphite particles.

Example 13: Preparation of Two-Dimensional (2D) Layered Bi₂Se₃Chalcogenide Nanoribbons

The preparation of (2D) layered Bi₂Se₃ chalcogenide nanoribbons iswell-known in the art. In the present study, Bi₂Se₃ nanoribbons weregrown using the vapor-liquid-solid (VLS) method. Nanoribbons hereinproduced are, on average, 30-55 nm thick with widths and lengths rangingfrom hundreds of nanometers to several micrometers. Larger nanoribbonswere subjected to ball-milling for reducing the lateral dimensions(length and width) to below 200 nm. Nanoribbons prepared by theseprocedures were subjected to graphene encapsulation using the presentlyinvented impact transfer method. The graphene-encapsulated Bi₂Se₃nanoribbons were used as a cathode active material for Na battery.Surprisingly, Bi₂Se₃ chalcogenide nanoribbons are capable of storing Naions on their surfaces.

Example 14: Preparation of Graphene-Encapsulated MnO₂ and NaMnO₂ CathodeActive Material for Na Metal Cells and Zn Metal Cells

For the preparation of the MnO₂ powder, a 0.1 mol/L KMnO₄ aqueoussolution was prepared by dissolving potassium permanganate in deionizedwater. Meanwhile, 13.32 g surfactant of high purity sodiumbis(2-ethylhexyl) sulfosuccinate was added in 300 mL iso-octane (oil)and stirred well to get an optically transparent solution. Then, 32.4 mLof 0.1 mol/L KMnO₄ solution was added into the solution, which wasultrasonicated for 30 min to prepare a dark brown precipitate. Theproduct was separated, washed several times with distilled water andethanol, and dried at 80° C. for 12 h. Some amount of the MnO₂ powderwas then subjected to the impact transfer treatment to obtaingraphene-encapsulated MnO₂ particles.

Additionally, NaMnO₂ particles were synthesized by ball-milling amixture of Na₂CO₃ and MnO₂ (at a molar ratio of 1:2) for 12 h followedby heating at 870° C. for 10 h. The resulting NaMnO₂ particles were thensubjected to ball-milling in the presence of MCMB particles and ZrO₂balls to prepare graphene encapsulated NaMnO₂ particles.

The MnO₂ particles, with or without graphene encapsulation, are alsoincorporated in alkaline Zn/MnO₂ cells. Graphene encapsulation was foundto dramatically increase the cycle life of this type of cell. TheZn-graphene/MnO₂ battery is composed of a graphene/MnO₂-based cathode(with an optional cathode current collector and an optional conductivefiller), a Zn metal or alloy-based anode (with an optional anode currentcollector), and an aqueous electrolyte (e.g. a mixture of a mild ZnSO₄or Zn(NO₃)₂ with MnSO₄ in water).

Example 15: Layered Zinc Hydroxide Salts Encapsulated by Graphene Sheetsas the Hybrid Cathode Material

The structural arrangements of dodecyl sulfate (DS) anions in theinterlayer space of layered zinc hydroxide salts (LZH-DS) and of thestructure of zinc hydroxide layers were investigated. As-prepared,highly crystalline LZH-DS has a basal spacing of 31.5 Å (3.15 nm). Aftertreatment with methanol at room temperature, zinc hydroxide layersshrank to form two new layered phases with basal spacings of 26.4 and24.7 Å. The shrinking was accompanied by a decrease in the content of DSanions in the interlayer space, indicating a change in the alignment ofthe intercalated anions and a decrease in the charge density of the zinchydroxide layers. This study indicates that tetrahedra Zn ions can bereversibly removed from the hydroxide layers, with the octahedrallycoordinated Zn ions left unaffected. This result suggests that layeredzinc hydroxide can be used as a Zn intercalation compound. In thepresent investigation, layered zinc hydroxide particles were alsosubjected to ball milling in the presence of natural graphite particlesand ZrO₂ balls, resulting in the formation of graphene-encapsulated zinchydroxide particles. It was discovered that graphene encapsulationimparts high-rate capability to the layered zinc hydroxide when used asa cathode active material of a Zn metal cell.

Example 16: Preparation and Electrochemical Testing of Various BatteryCells

For most of the anode and cathode active materials investigated, weprepared lithium-ion cells or lithium metal cells using the conventionalslurry coating method. A typical anode composition includes 85 wt. %active material (e.g., graphene-encapsulated Si or Co₃O₄ particles), 7wt. % acetylene black (Super-P), and 8 wt. % polyvinylidene fluoridebinder (PVDF, 5 wt. % solid content) dissolved inN-methyl-2-pyrrolidinoe (NMP). After coating the slurries on Cu foil,the electrodes were dried at 120° C. in vacuum for 2 h to remove thesolvent. With the instant method, typically no binder resin is needed orused, saving 8% weight (reduced amount of non-active materials). Cathodelayers are made in a similar manner (using Al foil as the cathodecurrent collector) using the conventional slurry coating and dryingprocedures. An anode layer, separator layer (e.g. Celgard 2400membrane), and a cathode layer are then laminated together and housed ina plastic-Al envelop. The cell is then injected with 1 M LiPF₆electrolyte solution dissolved in a mixture of ethylene carbonate (EC)and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v). In some cells, ionicliquids were used as the liquid electrolyte. The cell assemblies weremade in an argon-filled glove-box.

The cyclic voltammetry (CV) measurements were carried out using an Arbinelectrochemical workstation at a typical scanning rate of 1 mV/s. Inaddition, the electrochemical performances of various cells were alsoevaluated by galvanostatic charge/discharge cycling at a current densityof from 50 mA/g to 10 A/g. For long-term cycling tests, multi-channelbattery testers manufactured by LAND were used.

In lithium-ion battery industry, it is a common practice to define thecycle life of a battery as the number of charge-discharge cycles thatthe battery suffers 20% decay in capacity based on the initial capacitymeasured after the required electrochemical formation.

FIG. 4 shows the charge-discharge cycling behaviors of 3 lithium cellsfeaturing Co₃O₄ particle-based anodes: one cell containing un-protectedCo₃O₄ particles, a second cell containing reduced graphene oxide(RGO)-embraced Co₃O₄ particles (a prior art approach), and a third cellcontaining graphene-encapsulated Co₃O₄ particles produced by the instantimpact transfer method. It is clear that the presently inventedchemical-free production method leads to graphene-encapsulated Co₃O₄particles that exhibit the most stable battery cycle life. The cellcontaining unprotected Co₃O₄ particles has a cycle life of approximately150 cycles. In contrast, the cell featuring the graphene-protected Co₃O₄particles prepared according to the instant invention experiences only a5.7% reduction in capacity after 300 cycles.

Shown in FIG. 5 are the charge-discharge cycling behaviors of 2 lithiumcells featuring SnO₂ particle-based anodes: one containing un-protectedSnO₂ particles and the other containing graphene-encapsulated SnO₂particles produced by the instant impact transfer method using stainlesssteel balls. The present invention imparts a much stable cycle life to alithium-ion battery.

Shown in FIG. 6 are the charge-discharge cycling behaviors of 3 lithiumcells featuring micron-scaled (3 μm) Si particle-based anodes: one cellcontaining un-protected Si particles, a second cell containinggraphene-embraced Si particles produced by the indirect transfer method(with externally added milling media, ZrO₂ balls), and a third cellcontaining graphene-encapsulated Si particles produced by the directtransfer method (Si particles themselves being the graphene-peelingagent). Again, the invented graphene-embraced Si particles lead to verystable cycling behavior.

Example of the graphene-protected cathode active materials are presentedin FIG. 7 and FIG. 8. FIG. 7 has summarized the charge-discharge cyclingbehaviors of 2 lithium cells featuring lithium iron phosphate (LFP)particle-based cathodes: one containing un-protected LFO particles(mixed with 12% by weight carbon) and the other containinggraphene-encapsulated carbon-added LFP particles produced by the instantimpact transfer method (4% graphene+8% C). Again, the presently inventedmethod offers a better charge-discharge cycling behavior. FIG. 8 showsthe charge-discharge cycling behaviors of 3 lithium cells featuringLiV₂O₅ nanorod-based cathodes: one containing protected LiV₂O₅ nanorods(mixed with 10% by weight carbon black particles, one containinggraphene-embraced LiV₂O₅ nanorods produced by the impact transfer methodusing MoO₂ balls (approximately 5% graphene+7% C), and one containingLiV₂O₅ nanorods protected by a carbon matrix. The invention provides thebest approach to protecting the cathode active materials.

The invention claimed is:
 1. An impact-transfer method of producing agraphene-embraced or graphene-encapsulated electrode active materialdirectly from a graphitic material, said method comprising: a) mixingmultiple particles of a graphitic material, multiple particles of asolid electrode active material, and non-polymeric particles ofball-milling media to form a mixture in an impacting chamber of anenergy impacting apparatus, wherein said graphitic material has neverbeen previously intercalated, oxidized, or exfoliated and said impactingchamber contains therein no previously produced isolated graphenesheets; b) operating said energy impacting apparatus with a frequencyand an intensity for a length of time sufficient for peeling offgraphene sheets from said particles of graphitic material andtransferring said peeled graphene sheets to surfaces of said solidelectrode active material particles and fully embrace or encapsulatesaid particles to produce particles of graphene-embraced orgraphene-encapsulated electrode active material inside said impactingchamber; and c) recovering said particles of graphene-embraced orgraphene-encapsulated electrode active material from said impactingchamber and separating said non-polymeric particles of ball-millingmedia from said particles of graphene-embraced or graphene-encapsulatedelectrode active material.
 2. The method of claim 1, wherein saidnon-polymeric particles of ball-milling media contain milling ballsselected from ceramic particles, including ZrO₂ and non-ZrO₂ metal oxideparticles, metal particles, glass particles, or a combination thereof.3. The method of claim 1, further comprising a step of incorporatingsaid graphene-embraced electrode active material into a batteryelectrode.
 4. The method of claim 1, wherein an amount of residualgraphitic material remains after said step b) and said method furthercomprises a step of incorporating said graphene-embraced electrodeactive material and said residual graphitic material into a batteryelectrode wherein said residual graphitic material is used as aconductive additive in said battery electrode.
 5. The method of claim 1,wherein an amount of residual graphitic material remains after said stepb), and said step c) includes a step of partially or completelyseparating said residual amount of said graphitic material from saidgraphene-embraced electrode active material.
 6. The method of claim 1,wherein said particles of solid electrode active material containprelithiated or pre-sodiated particles having 0.1% to 54.7% by weight oflithium or sodium ions preloaded into said particles prior to step (a)of mixing.
 7. The method of claim 1, wherein said particles of solidelectrode active material contain particles pre-coated with a layer ofconductive material selected from a carbon, pitch, carbonized resin,conductive polymer, conductive organic material, metal coating, metaloxide shell, or a combination thereof.
 8. The method of claim 1, whereinsaid particles of solid electrode active material contain particlespre-coated with a carbon precursor material prior to step (a), whereinsaid carbon precursor material is selected from a coal tar pitch,petroleum pitch, mesophase pitch, polymer, organic material, or acombination thereof so that said carbon precursor material residesbetween surfaces of said particles of solid electrode active materialand said graphene sheets, and said method further contains a step ofheat-treating said graphene-embraced electrode active material toconvert said carbon precursor material to a carbon material and pores,wherein said pores form empty spaces between surfaces of said particlesof solid electrode active material and said graphene sheets and saidcarbon material is coated on said surfaces of solid electrode activematerial particles and/or chemically bonds said graphene sheetstogether.
 9. The method of claim 1, wherein said particles of solidelectrode active material contain particles pre-coated with asacrificial material selected from a metal, pitch, polymer, organicmaterial, or a combination thereof so that said sacrificial materialresides between surfaces of said particles of solid electrode activematerial and said graphene sheets, and said method further contains astep of partially or completely removing said sacrificial material toform empty spaces between surfaces of said solid electrode activematerial particles and said graphene sheets.
 10. The method of claim 1,further comprising a step of exposing said graphene-embraced electrodeactive material to a liquid or vapor of a conductive material that isconductive to electrons and/or ions of lithium, sodium, magnesium,aluminum, or zinc.
 11. The method of claim 1, wherein said particles ofelectrode active material are an anode active material selected from thegroup consisting of: (A) lithiated and un-lithiated silicon (Si),germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc(Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), andcadmium (Cd); (B) lithiated and un-lithiated alloys or intermetalliccompounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd withother elements; (C) lithiated and un-lithiated oxides, carbides,nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn,Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, or Cd, and their mixtures,composites, or lithium-containing composites; (D) lithiated andun-lithiated salts and hydroxides of Sn; (E) lithium titanate, lithiummanganate, lithium aluminate, lithium-containing titanium oxide, lithiumtransition metal oxide; and combinations thereof.
 12. The method ofclaim 1, wherein said electrode active material is a cathode activematerial selected from an inorganic material, an organic or polymericmaterial, a metal oxide/phosphate/sulfide, or a combination thereof. 13.The method of claim 12, wherein said metal oxide/phosphate/sulfide isselected from a lithium cobalt oxide, lithium nickel oxide, lithiummanganese oxide, lithium vanadium oxide, lithium-mixed metal oxide,lithium iron phosphate, lithium manganese phosphate, lithium vanadiumphosphate, lithium mixed metal phosphate, sodium cobalt oxide sodiumnickel oxide, sodium manganese oxide, sodium vanadium oxide,sodium-mixed metal oxide, sodium iron phosphate, sodium manganesephosphate, sodium vanadium phosphate, sodium mixed metal phosphate,transition metal sulfide, lithium polysulfide, sodium polysulfide,magnesium polysulfide, or a combination thereof.
 14. The method of claim1, wherein said electrode active material is a cathode active materialselected from sulfur, sulfur compound, sulfur-carbon composite,sulfur-polymer composite, lithium polysulfide, transition metaldichalcogenide, a transition metal trichalcogenide, or a combinationthereof.
 15. The method of claim 12, wherein said inorganic material isselected from TiS₂, TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, avanadium oxide, or a combination thereof.
 16. The method of claim 12,wherein said metal oxide/phosphate/sulfide contains a vanadium oxideselected from the group consisting of VO₂, Li_(x)VO₂, V₂O₅, Li_(x)V₂O₅,V₃O₅, Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃, Li_(x)V₆O₁₃,their doped versions, their derivatives, and combinations thereof,wherein 0.1<x<5.
 17. The method of claim 12, wherein said metaloxide/phosphate/sulfide is selected from a layered compound LiMO₂,spinel compound LiM₂O₄, olivine compound LiMPO₄, silicate compoundLi₂MSiO₄, Tavorite compound LiMPO₄F, borate compound LiMBO₃, or acombination thereof, wherein M is a transition metal or a mixture ofmultiple transition metals.
 18. The method of claim 12, wherein saidinorganic material is selected from: (a) bismuth selenide or bismuthtelluride, (b) transition metal dichalcogenide or trichalcogenide, (c)sulfide, selenide, or telluride of niobium, zirconium, molybdenum,hafnium, tantalum, tungsten, titanium, cobalt, manganese, iron, nickel,or a transition metal; (d) boron nitride, or (e) a combination thereof.19. The method of claim 12, wherein said organic material or polymericmaterial is selected from poly(anthraquinonyl sulfide) (PAQS), a lithiumoxocarbon, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, quino(triazene), redox-active organic material,tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,hexaazatrinaphtylene (HATN), hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-benzylidene hydantoin, isatine lithium salt, pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAQ), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof.
 20. The method of claim 19,wherein said thioether polymer is selected frompoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(1,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene](PTKPTB, orpoly[3,4(ethylenedithio)thiophene] (PEDTT).
 21. The method of claim 12,wherein said organic material contains a phthalocyanine compoundselected from copper phthalocyanine, zinc phthalocyanine, tinphthalocyanine, iron phthalocyanine, lead phthalocyanine, nickelphthalocyanine, vanadyl phthalocyanine, fluorochromium phthalocyanine,magnesium phthalocyanine, manganous phthalocyanine, dilithiumphthalocyanine, aluminum phthalocyanine chloride, cadmiumphthalocyanine, chlorogallium phthalocyanine, cobalt phthalocyanine,silver phthalocyanine, a metal-free phthalocyanine, a chemicalderivative thereof, or a combination thereof.
 22. The method of claim 1,wherein said electrode active material is a cathode active materialcontaining a mixture of an organic material and an inorganic material ora metal oxide/phosphate/sulfide.
 23. The method of claim 1, wherein saidelectrode active material particles include powder, flakes, beads,pellets, spheres, wires, fibers, filaments, discs, ribbons, or rods,having a diameter or thickness from 10 nm to 20 μm.
 24. The method ofclaim 23, wherein said diameter or thickness is from 1 μm to 10 μm. 25.The method of claim 1, wherein said graphitic material is selected fromnatural graphite, synthetic graphite, highly oriented pyrolyticgraphite, graphite fiber, graphitic nanofiber, graphite fluoride,chemically modified graphite, mesocarbon micro-bead, partiallycrystalline graphite, or a combination thereof.
 26. The method of claim1, wherein the energy impacting apparatus is a vibratory ball mill,planetary ball mill, high energy mill, basket mill, agitator ball mill,cryogenic ball mill, micro ball mill, tumbler ball mill, continuous ballmill, stirred ball mill, pressurized ball mill, plasma-assisted ballmill, freezer mill, vibratory sieve, bead mill, nano bead mill,ultrasonic homogenizer mill, centrifugal planetary mixer, vacuum ballmill, or resonant acoustic mixer.
 27. The method of claim 1 wherein saidgraphene sheets contain single-layer graphene sheets.
 28. The method ofclaim 1 wherein said graphene sheets contain at least 80% single-layergraphene or at least 80% few-layer graphene having no greater than 10graphene planes.
 29. The method of claim 1, wherein said procedure ofoperating said energy impacting apparatus is conducted in a continuousmanner using a continuous energy impacting device.
 30. A mass ofgraphene-embraced particles of solid active material produced by themethod of claim 1, wherein a graphene proportion is from 0.01% to 20% byweight based on the total weight of graphene and solid active materialparticles combined.
 31. A battery electrode containing saidgraphene-embraced or graphene-encapsulated electrode active materialproduced in claim
 1. 32. A battery containing the battery electrode ofclaim
 31. 33. A battery electrode containing said graphene-embraced orgraphene-encapsulated electrode active material produced in claim 1 asan electrode active material, wherein said battery is a lithium-ionbattery, lithium metal secondary battery, lithium-sulfur battery,lithium-air battery, lithium-selenium battery, sodium-ion battery,sodium metal secondary battery, sodium-sulfur battery, sodium-airbattery, magnesium-ion battery, magnesium metal battery, aluminum-ionbattery, aluminum metal secondary battery, zinc-ion battery, zinc metalbattery, or zinc-air battery.